The selection of processing parameters has great influence on the work-piece quality, processing time and processing costs. However the optimization of processing parameters is a complex nonlinear constraint optimization problem which is difficult to solve by traditional methods. In order to solve this problem effectively, this paper proposes a kind of improved electromagnetism-like mechanism (EM) algorithm. First, simplify the calculation process of the power and force and improve the power and force calculation formula to speed up the convergence speed and to enhance the search ability of EM algorithm. Then improve the particle movement formula by introducing movement probability. Meanwhile the Solis & Wets search algorithm is combined with the EM algorithm to improve the local search ability. For constrained optimization problems, a processing constraints method is developed by introducing a kind of feasibility and dominance rules into the EM algorithm. This improved EM algorithm is applied in the grinding parameters optimization problem and abrasive water jet machining parameter optimization problem. The results show that the proposed method is better than other algorithms and achieves significant improvement, which verifies the feasibility and superiority of this new algorithm.