In order to study the effect of grassland cover change on runoff yield and confluence process in Naqu Watershed, indoor artificial rainfall simulation experiment combined with data analysis method was used to study the change rule of surface runoff and interflow under grassland cover change by setting different scenarios such as slope and rainfall intensity. The results showed that with the increase of grassland coverage, the runoff generation time of surface runoff and interflow delayed gradually. The runoff generation time of surface runoff and interflow delayed by 19. 86% and 13. 36% respectively with the increase of grassland coverage by 20%. However, with the increase of grassland coverage, the cumulative amount of surface runoff decreases, and the interflow accumulation increases. For every 20% increase of grassland coverage, the cumulative amount of surface runoff decreases by 4. 69%, and the cumulative amount of the interflow increases by 6. 66%. Rainfall intensity, slope and grassland coverage are the main factors affecting runoff start time and runoff, but the contribution of rainfall intensity to runoff is the largest, followed by slope and grassland coverage.