Abstract: Aiming at the robot path planning problem in the synchronous welding of white car body,this paper proposes a grid method to establish the mathematical model of double synchronous welding robot.Firstly,an improved ant colony algorithm and a modified particle swarm optimization algorithm with crossover operator (MPSO) are made to realize the collision-free between welding robots.And then,the C space method is used to attain the collision-free between robots.Moreover,the better local and global paths are obtained and the comparing experiment is also made with standard ant colony algorithm and PSO algorithm.The result shows that the proposed MPSO has quicker convergence and shorter welding time.Finally,the simulations verify the feasibility of the proposed scheme for the dual-welding robots path plan.