Abstract: A specific two-bladed semi-open submersible sewage pump was selected as the research object for this study. Using the numerical simulation method, a comparative analysis was conducted on the transient radial force of the impeller under two types of variable speed operating conditions, namely ‘linear’ and ‘nonlinear’. The dynamic evolution law of the radial force during the variable speed process is revealed to investigate the force characteristics of the impeller during variable frequency speed regulation.The results indicate that the external characteristic curves exhibit basically the same trend during the start-up process. Under linear variable speed condition, the flow curve shows obvious start-up hysteresis. Under non-linear variable speed condition, each parameter can quickly reach the design value, which is more conducive to the submersible sewage pump entering the optimal operating condition rapidly. Regarding pressure stabilization fluctuation time, the nonlinear operating condition is achieved approximately 0.45 s earlier than the linear operating condition. The advantages of nonlinear speed regulation are thus verified, and the startup stabilization time of the equipment is shortened. Furthermore, under nonlinear operating condition, the distribution of the circumferential radial force on the circumference is more uniform than that under linear operating condition. A smaller load is consequently borne by the bearing, which greatly assists the operational stability of the pump.