Abstract: Based on the gravitational search algorithm (GSA), an effective modified gravitational search algorithm (MGSA) is proposed. Since the GSA divergence occurs during optimization process, the new strategy uses a limited velocity to control the particles and changes the parameters in the algorithm to improve this problem. The modified algorithm improves the exploration and exploitation ability significantly, and has better optimization ability. The performances of the MGSA and GSA are testified by MATLAB on a suite of eight benchmark functions, and the results are compared. Then the method is used to analyze slope stability. For this problem, the MGSA is used to search the critical slip surface and to calculate the corresponding minimum safety factor based on the limit equilibrium method. The simulated results illustrate that the MGSA has better optimization performance in searching the critical slip surface and calculating the safety factor compared with the GSA and other methods.