Bleached white sandstone represent the evidence of hydrocarbon migration in the northeastern Ordos Basin. Previous studies only focus on the chemical bleaching from the perspective of hydrocarbonrock interaction，but ignoring its forming environment. Bleached sandstones in study area only distribute in the weathered rock under the Jurassic unconformity，indicating unconformity played important role in the formation of bleached white sandstone. Combining field，petrographic，and geochemical analyses，the characteristics of unconformity structure were deeply investigated. The results show that the weathered clay zone is not developed in the Jurassic unconformity. The unconformity structure can be classified into two types：weathered rock zone developed（type Ⅰ） and nonweathered rock zone developed（type Ⅱ）. Sandstone in the upper part of weathered rock is composed of quartz and kaolinite，marked by secondary pores by dissolution，kaolinization of biotite，and loss of alkali and alkaline earth elements（K，Na，Ca，and Mg）. Kfeldspar content is higher in sandstone of the lower part of weathered crust，and biotite was partially weathered to hydrobiotite，K and Mg were retained in Kfeldspar and hydrobiotite. Pore fluid exchange was restricted in the finegrained sediments，with low porosity and permeability，causing weaker weathering process and hydrocarboninduced alteration. Kaolinite in white sandstone was the product of weathering process，rather than product of hydrocarbonrock interaction. Weathering enhanced the porosity and permeability of sandstone and oxidation during weathering led to the formation of iron oxides grain coatings，which changed the colour of sandstone from gray/green to red. Hydrocarbon reduction caused migration of Fe and bleaching of red weathered sandstone，which further decreased the degree of cementation after weathering. Hydrocarboninduced sandstone bleaching is a key record of hydrocarbon migration and accumulation in paleo weathered clastic rock.