Abstract: In order to evaluate in-service performance of high-speed trains, a new method for representing the running state of high-speed trains is proposed based on the multifractal spectrum parameters of the monitoring data is proposed in the paper. The multifractal spectrum of the monitoring data is calculated by using the multifractal theory. The relationship between the multifractal spectrum parameters and the train running states is analyzed, and the multifractal spectrum width Δα, the fractal dimension difference Δf and spectrum skewness k are selected as the characteristics of the high-speed train running states. Experimental results testify that the spectrum parameters can be used to characterize the running state of high-speed trains. When the train running states are changed, the multi-fractal spectrum parameters of the monitoring data are changed accordingly.