The existing methods for studying the dynamics, thermodynamics and deformation characteristics of screw pumps do not consider the coupling effect of multi field interaction, which deviates from the actual working conditions. Based on SolidWorks and ANSYS software, a three dimensional finite element model of a lead of conventional single screw pump is established in this paper. The influence of different gas GVF volume fraction on the temperature, pressure, deformation, leakage and volumetric efficiency of screw pump was studied by using the fluid thermal solid coupling method. The numerical simulation results of volumetric efficiency changing with the inlet and outlet pressure difference under pure liquid condition were verified by the published literature experimental data, and the optimal installation interference value was proposed. The results show that the GVF has an important influence on the comprehensive deformation of the rotor and pump bushing and the volumetric efficiency of the pump; the comprehensive deformation value of the rotor increases gradually from the inlet to the outlet, and increases gradually with the increase of the GVF ; with the increase of GVF, the comprehensive deformation value of stator first decreases gradually, and then increases sharply; with the increase of GVF, the leakage first decreases slowly, then increases rapidly, and the volumetric efficiency first increases slowly, then decreases rapidly; the numerical simulation results are in good agreement with the experimental values, and the average deviation is less than 7%.