Investigations and studies on the geology and geomorphology of the Upper Yangtze River indicate that the petrographic classification and composition of the gravel bed load in the river depends on the geological and geomorphological conditions of river basin. According to the regional geological and geomorphological characteristics and their effects on the lithologieal character of the gravel bed load the source of the gravel bed load can be divided into 4 supplementary regions, namely, the Middle and lower reaches of the Jinsha Valley and middle reaches of Yalong valley; the Upper reaches of the Mian Valley and the Dadu Valley; the Upper reaches of the Jialing and the Yangtze Gorges regions.After lithogical statistical analysis of nearly 125,000 grain samples collected by the author during his three geological and geomorphologial field investigation indicate that the lithologieal characters of the gravel bed load are governed by the geological and geomorphological conditions of the watershed. Hence, a mathematical model is set up to calculate the source of the bed load by using the percentages of petrographic classi-fication of the bed load in the main districts and the confluences of the valley (Eq. (2)). The result shows that 69.9% of the source of gravel bed load at Wanxian station, situated at the entry reach of the Groges, comes from the Middle and Lower reaches of the Jinsha valley and Middle reaches of Yalong Valley, 18% from the Upper reaches of the Mian Valley and the Dadu Valley, 12.1% from the Upper reaches of the Jialing Valley; and there are about 57.1% of the total gravel bed load at Yichang Sta-tion, which is located below the Gorges, comes from the Gorges Eegion itself, and 42.9% comes from the Upper Reaches above Wanxian Station.