Abstract: To prolong the economic life of an oil and gas field in the East China Sea, it was considered to drill an extended reach well through existing well, relying on the existing facilities. In this way, we could develop the reservoir of the midmountain pavilion in the southwest of the oil and gas field. By optimizing the casing fishing technology, successful completion of large-size long-distance casing fishing operation was successfully implemented, which laid the foundation of the subsequent lateral drilling of the ultra-deep extended reach well. With the further optimization of technologies including oil-based drilling fluid system, friction and torque control, hole cleaning, equivalent circulation density (ECD) control, and casing cementing, the drilling operation of the first ultra-deep extended reach well in the East China Sea was successfully completed.