Abstract: Risk Theta*: an any-angle path planning algorithm based on terrain risk is proposed in this paper. At first, based on statistical analysis on terrain feature of planetary surface, terrain risk index is proposed and the index map is built. Basic Theta* search is conducted on this index map to seek optimal path of lowest terrain risk. Simulation experiments show that the proposed algorithm could find out any-angle path of much lower terrain risk and comparable path length on grid map than A* and Basic Theta* which can significantly improve the rover safety, as well as satisfy the urgent demand of any-angle travel of planetary roving exploration, therefore it is fairly practical.