Lunpola basin is a Paleogene continental residual one and the only basin in Tibet with industrial oil discovery.Early exploration revealed that the thin oil distributed in the reservoirs with their buried depth more than1 500 m. However，the crude oil in new Well W1 at the depth of 1 800 m is still heavy，which indicates the complicated vertical zoning of crude oil in this basin. In order to clarify the geological origin of crude oil thickening and the favorable thin oil-enriched zone，physical properties，distribution rule and geological factors of crude oil thickening were studied comprehensively based on geological and geophysical data. The results show that the crude oil thickening in reservoirs of the Niubao Formation in Lunpola basin was mainly controlled by secondary alteration instead of low-mature oil. The reservoir of Well W1 locates under the oil-gas oxygenation level，which is 800 m below the unconformity surface. Structural interpretation and core observation show that the fractures and high-steep cracks of Well W1 are widely developed，for it locates in central fault region of central depression zone of the basin. This can lead to the loss of light components of the crude oil，so it is easy to be thickened. Thus the vertical zoning of the crude oil is clear.