Layer manufacturing time in laminated object manufacturing (LOM) technology is determined by the cutting speed and cutting path of each layer. When the parameters of cutting process such as cutting power and cutting speed are defined, the manufacturing time of each layer is determined by the cutting (scanning) path. So it is most important to optimize the cutting path in order to improve the manufacturing efficiency. In LOM technology, laser cutting path optimization is in fact vacancy course path optimization. The mathematical model of vacancy course path optimization is set up in this paper. Because of the complexity of solving the model, the two algorithms of grading planning are presented: start points in cutting contour are solved by using an improved nearest neighbor algorithm; when start points are determined, the problem of the path optimization turns into the traveling salesman problem (TSP), which is solved by using an high-efficiency intellectual biological algorithm-the ant colony system algorithm. The results of algorithm show that the algorithm remarkably shortens vacancy course in LOM and the manufacturing efficiency of rapid prototyping is improved.