In order to solve the problems of high viscosity gear pump,such as noise and short life,the factors affecting the internal pressure field of the pump were studied,including operating parameters of medium viscosity,rotating speed,output pressure and structural parameters of teeth number.Compared with common gear pump,the leakage effect of high viscosity pump is weaker,but the problems of unbalanced radial force,high noise and low life caused by trapped oil are more serious.The internal pressure field was fully simulated during the high viscosity gear pumps transportation process with CFD method.The results show that the pressure range of trapped oil increases with the increase of dynamic viscosity,and the rising rate has an exponential relationship with the dynamic viscosity;when the dynamic viscosity is 3 Pa·s,the rising rate is 70 MPa/s,and the dynamic viscosity is 30 Pa·s,the increasing rate is 877 MPa/s;the increase of rotational speed,output pressure and number of teeth has little influence on the pressure of the pump as a whole,but it can cause the rapid increase of the pressure at the trapped oil position.The trapped oil problem is the key factor to be considered in the optimal design of high viscosity gear pump.Increasing the size of unloading groove reasonably,reducing the speed and outlet pressure,and reducing the number of teeth are effective ways to solve trapped oil problems in high viscosity gear pump.