Based on the data of daily wind and specific humidity, surface pressure from NCEP/NCAR and the data of monthly average precipitation of 160 stations in China from National Climate Center, and according to correlation filed of precipitation with water vapor transport, the water vapor transport which is perpendicular to a cross section is defined as an objective indicator of vapor transport path, and six mainly vapor transport paths are found for North China. The results show that the confluent water vapor path, the water vapor path which outputs to the east, the water vapor path which inputs from the west and the water vapor path from the South China Sea have obvious inter-decadal variation, and the inter-decadal variation is basically the same as the inter-decadal variation of summer precipitation in North China. It is found that the water vapor path which outputs to the east and the water vapor path which inputs from the west have main influence on the precipitation in North China on summer though sliding correlation analysis. It is influenced by westerly. Second, the water vapor transport of water vapor path which is from the west of North China increases, at the same time which is from the southeast of the Pacific Ocean is enhanced obviously. Then water vapor which passes through the middle and lower Yangtze river and the South China and directly transports to the North China and Northeast China, results in heavy precipitation of North China and Northeast China and slight precipitation of the south and the Yangtze river. However, the water vapor from the bay of Bengal began to influence the precipitation in North China in summer from 2000.