In order to analyze aggregate gradation quantitatively,and reveal the relationship between fractal dimension D and passing ratio of key sieve and provide the control index of aggregate process,through the formula of mass fractal theory,calculating and analyzing the practical data,a method to accurately calculate fractal dimension of gradation was proposed,the limit of fractal dimension in use was obtained and the separation of gradation during construction was(evaluated) based on fractal dimensions.The results show that the fractal dimension has good correlation with the passing rate of 4.750 mm and could be used to evaluate the separation of gradation effectively.