This paper proposes a Segment Random and Angle Random (SRAR) algorithm for UAV′s three-dimensional route planning under complex space and multiple constraints.SRAR algorithm uses random segments and random angles to determine the way points.Meanwhile,the angle of directional line segment is specified,and the circular obstacle avoidance method,route smoothing method and multi-route planning method are designed to improve the quality of route planning,and meet the diversity requirements of route planning.This paper also proposes an unassociated iterative updating method to solve the variable-length solution,which can obtain the variable-length solution under multiple constraints.By verifying the route quality in complex space,and comparing with ant colony algorithm,genetic algorithm and particle swarm optimization algorithm,the results can effectively prove that the SRAR algorithm is robust,efficient and universal for UAV′s route planning.