Abstract: Based on the global model, within O- detachment process, the repetition frequency pulse relaxation model of high power microwave is rebuilt, and the relaxation process characteristics are analyzed. The relationship between electron density with time is simulated on different attachment frequency, detachment frequency and initial electron density. The results show that the electron density relaxation process is divided into the rapid-decay process and slow-decay process; electron density is significantly improved at the later stage of relaxation process. Detachment frequency and attachment frequency have opposite effects on the relaxation process. The higher the detachment frequency is, the higher electron density of the slow-decay process is, but electron density of the rapid-decay process doesnt change significantly. The higher the attachment frequency is, the sharper the change of the electron density on the rapid-decay process and the lower electron density in the slow-decay process is.