The traditional rain flow counting method is suitable for conventional fatigue, but it cannot retain the frequency information of vibration fatigue. Frequency is very important for vibration fatigue. Therefore, a frequency rain flow counting method is proposed based on the traditional rain flow counting method, which can effectively retain the frequency information. Spectrum developing process, and developing vibration fatigue load spectrum. Taking a certain type of engine test vibration signal as an example, determine the load classification to 0.5g, the vibration signal power spectrum, conventional load spectrum, and vibration fatigue load spectrum are developed It provides guidance for the subsequent vibration fatigue life assessment and reliability test of the main components of reusable engines. The results show that the prepared load spectrum can reflect the actual working load of the engine and meet the load spectrum requirements of the laboratory fatigue test .This paper presents a method for develop vibration load spectra suitable for the assessment of vibration fatigue life of similar structures in engineering. Keywords: vibration fatigue; load spectrum; engine; rainflow counting method; power spectral density