For the research on the method of building the load spectrum of ZLK50 type loader hydraulic system under the actual working conditions,a measurement scheme of multiple working conditions of the hydraulic cylinder is proposed based on the signal wireless acquisition mode.Statistic calculation of the time history of the bucket hydraulic cylinder load is carried out.Based on the statistical method of the rain flow matrix data in the shape of "from-to",a non-parametric frequency extrapolation method of the amplitude rain flow matrix based on kernel function estimation is introduced.According to the method,the eight stages’ program load spectrum of the bucket hydraulic cylinder in digging stage is established,and the program loading spectrum compilation on full operation stage of the hydraulic cylinder is finished.The data support for the fatigue life estimation of the loader hydraulic cylinder is provided.