Aiming at the problem that the influence of the vertical sloshing of the liquid in the medicine tank on the smoothness and operation quality of the whole machine is difficult to detect under the complex working conditions of the self-propelled sprayer with high ground clearance, based on the dynamic characteristics of the liquid sloshing and the equivalent criterion of the mechanical model, a spring-mass-damping equivalent mechanical model can describe the longitudinal sloshing of the liquid in the medicine tank, and the model parameters were solved by using the principle of mechanical equivalence. Fluent fluid simulation software was used to establish the liquid sloshing simulation model in the tank, and the simulation results were verified by bench experiments to reflect the real liquid sloshing impact. Using Matlab/Simulink software, a numerical analytical model of equivalent mechanics was established. Combined with the simulation results of Fluent, the changing law of the moment of liquid longitudinal sloshing acting on the container wall was compared and analyzed when the liquid filling ratio was 0.1, 0.5, and 0.9, and the established equivalent model was verified. The constructed equivalent mechanics model was applied to the analysis of the vertical dynamic characteristics of the sprayer, and it was concluded that the sloshing of the liquid medicine and the change of the quality of the liquid medicine had a great influence on the driving smoothness of the whole machine, and the driving smoothness of the whole machine was poor when the filling ratio was 0.8. The research results can provide an implementation approach for further research on the optimization of the chassis structure and the analysis of smoothness and stability under different operating conditions and time-varying liquid quality of the sprayer.