Abstract: In traditional CSMR method, the influences of fast exposed frequency, long existing cycle and large height difference of opencast mining slopes on the rock mass quality classification are not considered. The time influence factor is introduced firstly, and the angles between discontinuities and slope adjustment parameter and slope height coefficient are corrected. An improved CSMR method is put forward to classify the slopes of opencast mining with different heights, so as to increase the scope of application. The investigation of opencast mining slopes shows that the improved CSMR method is better than the traditional SMR and CSMR in practical situations, so that the improved CSMR is more reasonable for the classification of rock mass quality opencast mining slopes.