State-owned enterprises are a vital component of the state sector. Promoting both a reasonable increase in the quantity and an effective improvement in the quality of state-owned enterprise investment is key to leveraging the catalytic and multiplier effects of investment. Accountability for operation and investment is an accountability system established by state-owned asset supervision authorities at all levels, targeting the operational and investment acts of state-owned enterprises. However, as a major innovative measure of mandatory government regulation, how accountability for operation and investment affects the investment level of state-owned enterprises and whether it can promote reasonable investment growth have not been fully examined in the literature; research on its impact on the quality of state-owned enterprise investment also lacks an in-depth exploration of the underlying mechanisms. This study utilizes a sample of A-share listed companies on the Shanghai and Shenzhen stock exchanges from 2013 to 2023. By leveraging the exogenous shocks from the staggered implementation of accountability supervision policies across regions, a multi-period difference-in-differences model is constructed to systematically examine the regulatory effect of accountability for operation and investment on both the investment scale and quality of state-owned enterprises. Research finds that accountability for operation and investment can promote“dual improvement in quantity and quality”of state-owned enterprise investment, manifesting as a significant increase in investment levels and a substantive enhancement in investment quality in state-owned enterprises. Mechanism analysis demonstrates that accountability for operation and investment can enhance the investment levels of state-owned enterprises by improving management diligence and alleviating information asymmetry, and can improve the investment quality of state-owned enterprises by alleviating information asymmetry and enhancing internal control quality. Heterogeneity analysis based on differences in the characteristics of regulatory objects and subjects finds that the impact of accountability for operation and investment on the level and quality of investment in state-owned enterprises is more obvious in samples with poor internal financing capacity, low supply chain bargaining power, and high digital construction levels of State-owned Assets Supervision and Administration Commission. Economic consequences indicate that accountability for operation and investment enhancing the investment levels and investment quality of state-owned enterprises can effectively promote value creation. Compared with the existing literature, this study makes extensions in the following two aspects: First, by investigating both the quantity and quality of state-owned enterprise investment, this study provides more comprehensive empirical evidence on the effectiveness of accountability for operation and investment and expands the theoretical literature on accountability regulation at the financial level. Second, from the perspectives of managerial behavior and the organizational environment, this study systematically uncovers the mechanisms through which accountability for operation and investment affects the investment scale and quality of state-owned enterprises. This provides a deeper logical foundation for understanding this relationship and strengthens the theoretical comprehension of how government regulation influences the intrinsic mechanisms of corporate investment decisions. The findings also hold significant practical implications. This study focuses on the relationship between accountability for operation and investment and state-owned enterprise investment, systematically analyzing variation in effects based on the characteristics of both the regulatory objects and subjects. The findings not only offer important insights for regulatory authorities in differentially advancing the accountability system, optimizing the government regulatory framework, and enhancing regulatory effectiveness, but also provide decision-making references for how to promote the“dual improvement in quantity and quality”of state-owned enterprise investment and fully leverage the catalytic and multiplier effects of investment from the perspective of government regulation.