Abstract: This paper proposes a drilling parameter design and drilling fluid performance optimization method based on wellbore cleaning effect to address the complex problems of formation of rock debris beds and difficulty in cleaning the wellbore during the drilling process of extended reach wells in East China Sea oil and gas field, resulting in high frictional torque and even frequent occurrence of pump holding torque. Firstly, analyzed the main influencing factors of wellbore cleaning in extended reach wells, and used VIRTUALMUD software to optimize the engineering parameters such as drilling fluid displacement, mechanical drilling speed, and drilling fluid parameters such as 6 and 3 rotation readings that affect the wellbore cleaning performance of extended reach wells. Then, the performance of the oil-based drilling fluid used on site is improved by selecting suitable base oil, emulsifier, and barite. The optimized drilling parameters and drilling fluid system were applied in the extended reach well A, resulting in good wellbore cleaning effect and high rock carrying efficiency of the drilling fluid. During the operation, there were no complex situations such as stuck drilling, and the trip in and out of the well was smooth. The on-site application shows that this method has good feasibility and effectiveness, and is of great significance for improving drilling efficiency and reducing drilling costs.