Abstract: It is important for petroleum production engineer to know pressure variation regularity of a sucker rod pump, which could help analyze the dynamics of the rod at the bottom and apprehend the working condition of the pump. The fluid pressure in the pump barrel was measured by a dynamics rod detecting instrument. The study showed that the fluid pressure in the pump barrel was varied periodically. The fluid pressure in the pump barrel was for different stroke, where the pressure in the lower stroke was larger than that of upper stroke. The study also showed that the pressure in the pump barrel was affected by the leakage of the valves, and the fluid flow resistance between rod and tubing was very large.