Abstract: Crude oil from the Ordovician reservoir in block no.12 of the Tahe Oil Field belongs to extra-heavy oil due to high density.The crude oil has strong viscosity and seldom flows.Formation pressureand temperature are both high.In production,light oil is mixed in,and the mixing depth is about 5 500m.Extra-heavy oil underground sampling technique was optimized.PVT sampler was improved.Sam-ple heat and transfer device was designed.Qualified PVT sample was made 5 950 m deep for the firsttime,and then transferred and analyzed successfully.4 national records were made:highest samplingpYeSSUYe,blggeSt VISCOSIty,highest temperature,and deepest depth.A set of extra-heavy oil under-ground sampling technique was concluded.