As the weathering of the Tibetan Plateau may affect the global carbon cycle and the long time-scale climate change, its weathering rate and influential mechanism have been subjected to the attention of the scientific community. In this study, the Jinshajiang River, the Lancangjiang River and the Nujiang River originating from the Eastern Qinghai-Tibet Plateau were monitored for one hydrological year and water samples were collected every other week. By analyzing basic physical and chemical properties, the pH of river water samples turn out to be mildly alkaline and the chemical composition have a noticeable seasonal variation. During the research, we used forward model to calculate the contribution of different end-members to the river water chemistry and net CO_2 consumption rates by silicate weathering, around 76.3*10~3 mol/(km~2?a),182.0 *10~3 mol/(km~2?a) and 238.9 *10~3 mol/(km~2?a) of the upper reach of Shigu (the Jinshajiang River), Weideng (the Lancangjiang River) and Liuku (the Nujiang River), respectively, the net CO_2 consumption rate in rainy season can be twice to four times than that in dry season. At last, we used the inverse model to calculate the net CO_2 consumption rate, and the results appeared to be quite good (within 25%).