The throttle pressure reducing valve has potential for the high pressure heat exchanger with the advantage of simple structure, easy operation and maintenance. We investigated the discharge capacity under different pressure difference between inlet and outlet, the area of inlet and throttle though CFD simulation and validating experiments. A theoretical formula of the discharge capacity was developed through the theoretical analysis and simulated results and was well proved by the experiments. The results revealed that the square of discharge capacity is positively proportional to the pressure difference, and the drag coefficient has a linear relationship with the throttle area and the reciprocal of flange area. This research establishes the theoretical basis for the designing and engineering application of throttle pressure reducing valve.