A kind of new equipment and method was put forward to test the pressure sensitivity of polymer melt. The viscosity of low density polyethylene was studied. Through the method of constant shear rate, the constant shear stress method and the superposition method, the viscosity pressure sensitivity coefficient of LDPE was calculated, the difference of the three method was compared, and the influence of pressure on the LDPE melt viscosity was studied. The viscosity pressure sensitivity coefficient calculated by constant shear rate method changes with the shear rate and there is a big error. The pressure sensitivity coefficient is accurately calculated by constant shear stress method and the value is constant. The pressure sensitivity coefficient calculated by the superposition method is also accurate, but the method is complex.