This paper presents a novel simple, but efficient robot path planning algorithm, which plans the obstacleavoidance path according to map information, makes robots reach the target. In the paper, the actual environment is discretized into a topologically organized map consisting of targets, obstacles and free spaces. We quantify the road roughness, which affects the motion of robots to the degree of pass convenience with a special mathematical model, and introduced into the model for path planning. Targets propagate the socalled "vector-distance" to whole workspace through free-space grid points in a special direction. Because the distance propagating in this way has direction and size, it is called "vector-distance", which is constrained by the motion of nonholonomic mobile robot. So the path obtained by this algorithm is the optimal path suitable to the motion of nonholonomic mobile robot. This model is characterized by high computational efficiency, small storage cost and perfectly simulating the actual map. This algorithm can be conveniently used in practice.