Abstract: In the light of the geological characteristic of ultra-deep strata reservoir of Tahe Oilfield and crude oil property, taking heavy oils in the TK1073, TH10227 and TH12312 wells and 4 kinds of Tahe thin oils as research objects, rheological characteristics and viscosity-temperature characteristics of crude oil are tested and analyzed by rheological methods.viscosity reduction effects of difierent Tahe heavy oils respectively mixed with different volumes of Tahe thin oils, including No.1 Oil Production Plant DK4, No.1 Multi-purpose Station, No.1 and No.2 mixed oils are evaluated.The applicability of light oil and mixed medium-density oil to the thinning of Tahe heavy oil is discussed to expand thin oil sources and save light oil.Research results indicate that heavy oil in TK1073 and TH12312 wells are extremely heavy oils and heavy oil in TH10227 well is extra heavy oil, of which production and gathering must be given thin oil mixture and other thinning measures.No.1 Oil Production Plant DK4 light oil, No.1 Multi-purpose Medium-density Oil and No.1 Mixed Medium-density Oil are provided with the better applicability to the thinning of Tahe heavy oil by blending with thin oil, while No.2 Mixed Medium-density Oil is relatively poor.Reliability of laboratory study conclusions are confirmed by actual applications.