Abstract: The condition and gradient of the slope, the block shape and mass of the rock block are the major factors affecting the movement characteristics of rock-fall. Through the orthogonal test design(L27(34)),the sort of them is obtained: slope condition X1,rock block shape X2,slope gradient X3,rock block mass X4.The velocity estimation values of rock-fall are calculated with the velocity equation v=-7.85X10.50+0.47X23.22+2.97X30.24.This equation is established by regression analysis. The values are compared with the measured values. The results show that the relative error is only 8.2% and the correlation coefficient is r=0.92. Trend impact of regression equation analysis of the single factor shows that the slope condition has significantly negative linear correlation relationship with the speed of rock block. The mathematical relationship between the rock block shape and speed is sunken curve. The slope gradient and speed is convex curve. They are the same as the analysis of the empirical formula. Through rock-fall field test and based on the measurement, a simplified modified velocity formula is v =v0+(L/2.45)vc.By comparison, it is in good agreement with the measured results. It proves the applicability and validity of the formula given in this paper. The results can be used in estimating the speed and the impact energy of the rock-fall, and have a certain reference value in choosing prevention and control measures of rock-fall.