Abstract: A series of analyses, including major and trace element analysis, X-ray diffraction for bulk and clay mineral composition, Rock-Eval analysis, TOC analysis and scanning electron microscope observation, were conducted in order to determine the different silica sources and hydrocarbon accumulation between the Chang 7 member and Chang 9 member shale of the Triassic Yanchang Formation in the Ordos Basin. The Chang 7² sub-member and the Chang 9 member shale had more similarities in silica sources, mineral composition, element composition and organic geochemical characteristics, while the Chang 7³ sub-member shale showed certain differences in the above properties from the other two sets of shale reservoirs. The silica in the Chang 7² sub-member and the Chang 9 member shale came from terrestrial detritus, while the silica in the Chang 7³ sub-member shale showed the characteristics of two sources, namely, terrestrial detritus and hydrothermal from vents at the bottom of the lake. Both Chang 7 and Chang 9 shales are high-quality source rocks. However the contents of residual hydrocarbon and kerogen are higher, the type of kerogen is much better, and the oil saturation index is higher under the influence of hydrothermal fluid for the Chang 7³ sub-member shale. Hence the Chang 7³ sub-member is superior to the Chang 7² sub-member and Chang 9 member shale and has higher exploitation value.