Abstract: Extra-heavy oil is featured with gelatination, high content asphaltene, high viscosity, high density and poor flowability. At present, viscosity reducer is mainly used to cut down its viscosity. However, the solution of viscosity reducer will probably tend to corrode oil pipeline. In allusion to the property of extra-heavy oil produced from Henan Oilfiled, orthogonal experimental method is adopted to research the viscosity reducing effectiveness of emulsified viscosity reducer AE and EC and oil-soluble viscosity reducer AC. Static corrosion weight loss method are applied to evaluate the corrosion level of the above 3 viscosity reducers on N80 steel in order to select appropriate candidate. Results from the orthogonal experiment display that the best viscosity reducer is EC with a 99.81% of viscosity reducing rate when it is used at 70 ℃ with a 0.3% of addition volume and a 6:4 of oil-water ratio; results from corrosion experiment show that AE and EC have sound corrosion inhibitation effectiveness and the corrosion inhibitation rates of the two reducers are up to 80.42% and 85.85%, respectively.