Objective Ultrafast lasers acting on liquid media can generate higher energy terahertz waves compared with gaseous and solid media and the related research work has been relatively perfect in experiments while the theoretical aspect lacks a complete explanation process. The physical mechanism of the transient photocurrent model was discussed in detail through the process of step-by-step establishment of the model and the conversion efficiencies of four solutions such as water and acetone to terahertz under different parameter conditions were investigated through this model. Methods Taking water molecules as an example a three-level system was constructed based on the ionization principle on the basis of the traditional photocurrent model. The ionization relaxation time was determined by the ionization potential of water molecules and the ionization rate and current intensity of water molecules were determined by associating the ionization time with the third-order nonlinear polarization rate. A complete transient photocurrent model of liquid solution was then constructed and applied to study the effect of different laser parameters on the terahertz radiation energy in four liquids including water and acetone under two 800 nm Gaussian light fields. Results The stronger the electric field intensity the higher the resulting molecular ionization rate and the higher the corresponding terahertz conversion efficiency. At a given laser intensity the strongest terahertz radiation energy corresponded to an optimal pulse width and pulse delay in the sub-picosecond order. In addition the energy difference and time-frequency spectrum characteristics of terahertz radiation in water and acetone solutions were further compared and the results showed that the radiation yield of acetone was always the highest. Conclusion In liquid media the energy of terahertz radiation is affected by various aspects such as the ionization potential of the medium absorption coefficient molecular density etc. which likewise illustrates and validates the superiority of acetone over water heavy water and ethanol in terms of the combined performance parameters. In this paper the intensity of terahertz radiation in different liquid states is investigated using photocurrent model which provides a reference for understanding the radiation in other liquid media as well as for experiments.