Abstract: Based on Fractal Brownian Motion (FBM) model,tracking residual data for vehicle is processed.According to the characteristics of the data,a new method to get the scale interval is present,which is more accurate.Simulating and actual results show that the method has high precision and is easily used in practise.Using FBM model and the method the fractal dimensions for many data are estimated.The results show that fractal dimension of data from tracking vehicle by firing liguid is less than that by firing solid.