Abstract: The Tahe oilfield is an ultra-deep and super-heavy oil field. Due to the high viscosity of heavy oil, light oil is mixed in for production. As dilute pump pressure fluctuates during production, the viscosity of mixed oil changes obviously, leading to the discontinuous outflow at wellhead and the low accuracy of oil production estimation, which are unfavorable for production evaluation and daily management. Through the analysis of the working principles of light oil mixing wells in the Tahe oilfield, taking into consideration of the leaking characteristics of large-gap pumps under different viscosities, combining with different volume coefficients in different blocks, we calculated the suction amount during the operation of the pumping unit by the effective stroke of the oil boom, and further calculated liquid production quantity, which guided the daily management of light oil mixing wells.