Abstract: During the artificial lift to Xinjiang deep heavy oil reservoir, crude oil gradually losing mobility with temperature decreasing is a serious problem. The light oil blending is an effective way to reduce wellbore friction. In this work, the indoor simulation measurement device was built according to the in-situ light oil mixing technique to study the light oil and its dynamic mixing process during the process of light oil addition. And then variation of the mixture viscosity with the decrease of wellbore temperature is also measured. Combined with the wellbore heat transfer and fluid flow model, the wellbore friction is calculated and analyzed under different light oil ratios. Study results show that the increase of the light oil ratio is able to decrease the friction effectively, but the contribution of unit light oil for friction fall decreases with the rise of light oil ratio.