Now in the development of oilfields, it is far from enough to determine only the sedimentary facies of sandbodies, and the width, length and other parameters of the sandbodies should be predicted precisely.—This is quantitative study of sedimentary facies referred to in this paper. On the basis of drilling data and fine division and correlation of strata, quantitative study  was made on the sedimentary facies of the lower member of Lower Tertiary Xiaganchaigou Formation of Shaxi Oilfield, Qinghai Province. The lower member of the Ganchaigou Formation consists of clastic rocks, about 250m thick. It is divided into four oil-containing formation sets, i.e. I, II, III and IV. Formation set IV is deposited in delta plain environments of a braided river delta, and formation sets I, II and III are deposited in delta plain environments of a meandering river delta.  In the delta plain of the braided river delta, sandbodies are mainly deposited in distributary channels. These sandbodies are wide ribbons in shape and SW-NE in trend. They are commonly 1200-3000m wide and 5-10m thick. Their width/thickness is commonly 200-280. In the delta plain of the meandering river delta, sandbodies are mainly deposited in distributary channels. These sandbodies are narrow ribbons in shape. They are commonly 400-700m wide and 3-6m thick. Their width/thickness is commonly 80-110. Sandbodies of the braided delta plain are wider and thicker than those of meandering delta plain. This is because frequent shifting of braided distributary channels leads to lateral combining and vertical superimposing of sandbodies. Due to diffenrent width of sandbodies of different facies,  inter-well distance of development wells should be different for braided delta plain and meandering delta plain.