Promoting moderate-scale management of land has been the only way for China’s agricultural modernization, and promoting the continuous increase of farmers’ income has been an objective requirement for achieving common prosperity. In July 2023, the Ministry of Agriculture and Rural Affairs issued the Guiding Opinions on Safely Carrying out Pilot Work on Solving the Fragmentation of Contracted Land, which emphasized exploring solutions to cultivated land fragmentation while focusing on the relationship between farmers and land. The Central Rural Work Conference of the same year stressed, “to build a strong nation, we must first strengthen agriculture; only when agriculture is strong can the nation be strong”. Currently, China is in a transitional period from traditional agriculture to modern agriculture, and the planting industry remains the primary livelihood for most farmers. As the backbone of ensuring national food security and promoting rural revitalization, promoting sustained income growth for planting-dominant farm households is an objective requirement for solidly advancing common prosperity. Therefore, in this context, studying the specific impact of cultivated land fragmentation on the income of planting-dominant farmers has become a hot topic for discussion. To this end, this paper constructs an analytical framework and empirically tests the impact of cultivated land fragmentation on the income of planting-oriented farmers based on 12 rounds of panel data from the National Rural Fixed Observation Points from 2009 to 2020. The research findings are as follows: (1) Cultivated land fragmentation significantly reduces the income of farm households engaged in planting. This conclusion still holds even after a series of robustness tests. (2) The results of the moderation effects test show that the “non-grain production” of crop planting and the development of farmland transfer markets can significantly weaken the inhibitory effect of cultivated land fragmentation on the income of farm households engaged in planting. (3) Heterogeneity analysis reveals that the inhibitory effect of cultivated land fragmentation on farmers’ income is more pronounced in villages with high levels of fertilizer application intensity, aging populations, and located in hilly mountainous areas. Therefore, this paper believes that the problem of fragmented and inefficient use of cultivated land should be solved from the aspects of improving the circulation market of cultivated land, improving the comparative income of grain production, and promoting the reduction and efficiency of chemical fertilizers, so as to promote the development of agricultural modernization and achieve common prosperity. It should be pointed out that with the development of agricultural socialized services, the meaning of cultivated land fragmentation may change. In other words, adopting land trusteeship methods such as “contracting rights remain unchanged and management rights are contiguous” will change the pattern of original property rights fragmentation and reduce the degree of fragmentation of cultivated land. However, this paper is unable to observe and discuss this situation due to data limitations, which is also the deficiency of this paper and the direction of future research extension and deepening.