The Longmen Mountains are located in the eastern margin of the Qinghai—Xizang (Tibet) Plateau. It is not only the one which has the greatest transmutation of steepness among those around the Qinghai—Xizang(Tibetan) Plateau, but also one of the areas where the strongest climate and tectonic activities have been happened. Thus, Longmen Mountains area has been one of the best places to study the relationships about tectonic—geomorphy—water system. With the ASTER—GDEM date, this article extracts the 15 longitudinal profiles of bedrock channels of the Eastern Qinghai—Xizang(Tibet) Plateau, and fits the longitudinal profiles with the simple mathematical function, then analyzes the topographic feature combined with stream power incision model in different regions of the Longmen Mountains. The study draws the following conclusions: ① based on the analysis of longitudinal profiles, the Longmen Mountains have high uplifting rate, which leads to the stronger river erosion in this area; ② in the central and southern sections of the Longmen mountains, most of logarithmic S—A plots are convex upward, therefore, these region have not been achieved the equilibrium state and are in the period of pre equilibrium; ③ in the northern section of the Longmen Mountains, most of logarithmic S—A plots are straight lines, therefore, this region has been achieved the equilibrium state and is in the period of equilibrium; ④ the characteristics of drainage development in different regions of the Longmen Mountains show that the central and southern sections of the Longmen Mountains have the stronger tectonic activity and the higher uplifting rate; while the northern section of the Longmen Mountains has the weaker tectonic activity and the lower uplifting rate, which reflects the uplift of Eastern Qinghai—Xizang(Tibet) Plateau very different among areas.