In the engine test, the fluctuating pressure data of the thrust chamber is an important basis for studying the performance of the engine and judging the unstable combustion. In view of the characteristics of engine test fluctuating pressure data and the shortcomings of traditional fourier transform in the field of time?frequency analysis, the engine test fluctuating pressure data are analyzed according to the advantages of empirical mode decomposition (EMD) method, such as good adaptive characteristics, accurate positioning of instantaneous frequency, local instantaneous expression ability and extraction of signal components. The method and steps of analyzing fluctuating pressure data by EMD method are introduced. FFT method, EMD decomposition and wavelet analysis method based on different wavelet basis functions are used to analyze fluctuating pressure data respectively. The shortcomings of FFT and wavelet analysis methods in analyzing nonlinear and non-stationary data are summarized. The results show that the EMD method can well analyze the nonlinear and non-stationary data of fluctuating pressure. This method has important application and popularization value for studying and analyzing the frequency spectrum characteristics of engine test fluctuating pressure data and unstable combustion.