With the help of Comsol software, the distribution of magnetic field intensity and flow field inside and outside the focusing tube was simulated. The distribution law of magnetic field intensity was analyzed as well as the mechanism of magnetic field acting on water jet, and the optimum magnetic field intensity was obtained to achieve the best focusing effect of water jet. The results indicate that the best focusing effect of water jet was obtained with the current of 2.2A. The difference of flow field outside the nozzle was observed and analyzed before and after the magnetic field was applied, the vibration and dynamic signal acquire analysis system (CRAS) was used to measure the actual impact force of water jet. The experiment results show that with the magnetic field applied, the effective diameter of abrasive water jet decreases, the focusing effect increases obviously, the original water mist disappears, and the impact force of abrasive water jet increases with the increase of current intensity.