Abstract: Hydraulic oscillators are effective against high friction and serious back pressure during the drilling of wells with complex structures. However, conventional hydraulic oscillators suffer from high pressure loss, which leads to the failure of pumps on the ground due to overloaded operations. For this reason, conventional hydraulic oscillators were optimized structurally by a variety of approaches, including adding a fixed piston in the oscillation sub, increasing the diameter of the flow hole of the eccentric valve, arranging a flow duct at the transition area between the spline end and the bottom of the spline shaft. These measures increased the feedback area and flow area of the piston and reduced the energy loss of hydraulic oscillators. In this way, an enhanced hydraulic oscillator with low pressure loss was developed. Laboratory test results indicated that the hydraulic oscillator had measurably reduced the pressure drop, meeting design requirements. In addition, field tests were carried out in Well Yi184-X37 of Shengli Oilfield. All indicators satisfied design and operation requirements. The developed hydraulic oscillator addressed back pressure issues, increased the rate of penetration (ROP), and demonstrated a pressure drop much lower than that of conventional hydraulic oscillators. The research results show that the enhanced hydraulic oscillator with low pressure loss have a low pressure drop and can effectively solve the difficulties of serious back pressure and high friction, thus meeting the needs of safe and efficient drilling of wells with complex structures.