Abstract: The microwave window of 2.45 GHz electron cyclotron resonance (ECR) ion source is a lossy component when it works on intense ion beam DC mode, resulting in limited service life. In order to study the damage mechanism of microwave window, the finite element software was used to calculate the temperature and stress distributions of Al₂O₃ ceramic microwave window under the effect of the microwave, plasma and backstreaming electrons. The calculation result shows that the maximum Von Mises stress is at the edge of the microwave window under the effect of microwave and plasma, while under the effect of the electron beam, the largest stress is at the center of the microwave window. Enhancing water-cooling performance can reduce the influence of microwave and plasma on microwave window, and increasing thickness of BN can protect the window from electron beam more effectively. The combination of these two methods is feasible and effective in practice to extend the service life of the ECR ion source.