Abstract: Such as side attrition of pumping rods and tubes problems often encountered when the conventional oil pumping unit is used for inclined wells production. To solve the technical problems, a new liquid power assisted rodless oil pumping system is developed based on hydraulic principle. The novel system can completely solve the rod-tube side attrition problem, and is especially applicable used in inclined wells. This system includes ground hydraulic driving system, power transmission system and down-hole hydraulic oil pumping system. Its workflow is introduced in this paper. In-site test has smoothly run over 18 months which indicates the system can fully meet the oil field production requirements.