Abstract: During the lifting process, with the decrease of wellbore temperature, the viscosity of crude oil increases continuously, the fluidity becomes poor and the lifting becomes more difficult. Dilution can reduce the viscosity of wellbore crude oil and effectively reduce the lift friction, which is a common process for wellbore viscosity reducing. According to the process flow of in-situ mixing of light and heavy oil in Chunguang oilfield, an indoor evaluation device for heavy oil wellbore flow was established to simulate the dynamic mixed process of light and heavy oil in the process of casing mixed with light and heavy oil. Through the experiment,the change characteristics of the injection rate and water cut of the casing flow resistance under different temperature conditions were measured, the viscosity change and viscosity reducing rate under different mixing ratios were simulated, and then a set of corresponding diagrams of the relationship between oil production volume and oil production temperature and dilution ratio was formed, which provided a basis for effectively guiding the field application of wellbore dilution viscosity reducing process.