Aimed at the problem of positioning to an arbitrary point in the travel was not able to be precise of the general rotary cylinder at present，a pneumatic rotary servo cylinder was developed. The control subsystem of the rotary servo cylinder was constructed, and the controlled characteristics of rotary servo cylinder were analyzed. Research on the damping angle was predicted by using BP neural network, in order to effectively suppress the disturbance during positioning and achieve precise positioning, and the control strategy was proposed by using dynamic compensation to damping angle. The performance test results of the cylinder showed that by using the control strategy of damping angle dynamic compensation, the features of pneumatic high speed of the cylinder were not only kept, but also the cylinder was able to be positioned rapidly and precisely to an arbitrary point within range. The experiments show that damping positioning can all be achieved in 0.15 s, with smooth speed and without dynamic mutations, and the actual displacement is without overshoot and non-oscillation. The positioning error is within ± 1.0°.