In the process of capacity regulation of reciprocating compressor, the frequent change of inlet temperature and pressure makes the control of exhaust flow unstable, resulting in the high pressure ratio of the intermediate stage.At last the compressor cannot operate safely.To solve the problem, a novel flow control scheme based on inlet temperature and pressure ratio is proposed.In this scheme, the intake model of the cylinder under the capacity regulation condition is established to calculate the load of the first cylinder.Then, the adaptive predictive PID( APPID) controller is designed to con-trol the pressure ratio of other stages, and the grey prediction model is used to predict the pressure output to overcome the system delay.To solve the problem of control parameters tuning, an im-proved particle swarm optimization ( PSO) algorithm is adopted to obtain the optimal control parame-ters.The effectiveness of the adaptive predictive PID control method is verified by a two-stage com-pressor model simulation.Finally, the flow control scheme is applied to the actual four-stage air re-ciprocating compressor flow control system.Although the temperature difference is greater than 15℃, the compressor exhaust flow is maintained at the set value and the pressure ratio is also main-tained stable.At the same time, the compressor pressure ratio can be quickly adjusted without over-shoot.The application result further verifies the feasibility and effectiveness of the scheme.