Based on vegetation type map， leaf area index and meteorological data for northern Xizang from 1990 to 2019， the relationship between the transition zone of alpine meadow and alpine grassland in northern Xizang and dry-wet climate boundary （1.5 on the dry-wet index， which is the boundary between semi-arid and semi-humid regions） and 400 mm Isohyet was compared to explore the response characteristics of vegetation distribution to different dry-wet boundaries.The results show that the precipitation in northern Xizang decreases from southeast to northwest， the dry-wet index increases， and the surface evolves from wet to dry； from 1990 to 2019， the precipitation increases， and the dry-wet index decreases， showing a wetting trend； the annual LAI value of vegetation increased significantly， indicating that the environment for vegetation growth in 30 years has been improved， and the improvement degree of alpine meadow is higher than that of alpine grassland； the consistency between dry and wet climate boundary and the transition zone of alpine meadow and alpine grassland is high， indicating that the dry wet index can better characterize the vegetation distribution in northern Xizang， while the 400 mm Isohyet is generally to the West； LAI in the east of dry wet boundary is more than 0.6， and LAI in the west of 400 mm Isohyet is less than 0.1； from the correlation analysis among annual LAI value， annual precipitation and annual dry wet index， the increase of precipitation and wet surface conditions in most areas are conducive to vegetation activities.