The separate and joint effects of the Great Khingan Strip (GKS) and Changbai Mountain (CM) on summer rainfall in Northeast China are investigated based on high resolution simulations using a regional numerical model WRF-ARW (V3.9). The results indicate that the GKS and CM can significantly influence rainfall and atmospheric circulation in Northeast China. The two mountains block the southerly winds at the windward slopes, leading to moisture convergence and upward movement over the regions; therefore, summer rainfall increase on the windward slopes of the two mountains. On the leeward slopes, there are moisture divergence and downward motion of winds, which results in decreased precipitation over the regions. The existence of the GKS can increase summer rainfall by about 1.09 mm d^-1 (30% of climatological mean summer precipitation in control run) in the region from the eastern slope of the GKS to the Songnen Plain, but decrease it by about 0.69 mm d^-1 (24% of climatological mean summer precipitation in control run) over Eastern Mongolia. The existence of the CM can increase summer rainfall by about 1.76 mm d^-1 (26% of climatological mean summer precipitation in control run) in the region from the southern slope of the CM to the Korean Peninsula, but decrease it by about 0.81 mm d^-1 (22% of climatological mean summer precipitation in control run) over the Sanjiang Plain. The combined effect of the GKS and CM has an offset effect on summer rainfall in Eastern Mongolia, the Songnen Plain, and the Korean Peninsula, but has an enhancement effect on the Sanjiang Plain. The results of this study are important to better understand the formation of the current summer climate in Northeast China.