Twin-screw multiphase pumps experience a severe decrease in efficiency, even the breakdown of pumping function, when operating under wet gas conditions. Additionally, field operations have revealed significant vibration and thermal issues which can lead to damage of the pump internals and expensive repairs and maintenance. There are limited models simulating the performance of twin-screw pump under these conditions. This project develops a pump-user oriented simulator to model the performance of twin-screw pumps under wet gas conditions. Experimental testing is conducted to verify the simulation results. Based on the simulations, an innovative solution is presented to improve the efficiency and prevent the breakdown of pumping function. A new model is developed based upon a previous Texas A&M twin-screw pump model. In this model, both the gas slip and liquid slip in the pump clearances are simulated. The mechanical model is coupled with a thermodynamic model to predict the pressure and temperature distribution along the screws. The comparison of experimental data and the predictions of both isothermal and non-isothermal models show a better match than previous models with Gas Volume Fraction (GVF) 95% and 98%. Compatible with the previous Texas A&M twin-screw pump model, this model can be used to simulate the twin-screw pump performance with GVF from 0% to 99%. Based on the effect of liquid viscosity, a novel solution is investigated with the newly developed model to improve the efficiency and reliability of twin-screw pump performance with GVF higher than 94%. The solution is to inject high viscosity liquid directly into the twin-screw pump. After the simulations of several different scenarios with various liquid injection rates and injection positions, we conclude that the volumetric efficiency increases with increasing liquid viscosity and injecting liquid in the suction is suggested.