Based on wavelet packet analysis and probability density function analysis, the characteristics of signal fluctuation and probability density function distribution of the first compressor stator casing wall static pressure, which was measured during the throttling process of a certain engine, are investigated. It is observed that along with the gradual approaching of engine working point to the surge line, the fluctuation magnitude of the first compressor stator casing wall static pressure contents at several specific frequency bands will increase, and corresponding probability density function distribution will become wider. The observed signal characteristics can serve as an aerodynamic instability indication of the test engine during the throttling process.