When using airpressure method to test the performance of ａ highp ower hydraulic impactor, an obvious error in measurement will be produced due to the distortion of air pressure transfer. In this paper, the transfer function o f the airpressure testing system is obtained ｂｙ ｕｓｉｎｇ ａ lossless mode l of ｉｔｓ pneumatic pipe sensing system. Based on this, a further study on the structure size of the pipe is done and then the effects of the resonant frequen cy and transient pressure reciprocating reflection change of the pipe on measure ment error are analyzed in theory. A comparison of the test results of two tes ting systems with different structure sizes used to test impact performances of a highpower hydraulic rock breaker TB725X indicates that the theoretical analy sis agrees with the test results fairly well. The work in the paper provides an effective way to design an airpressure testing system for measuring the perfor mance parameters of an impactor.