Abstract: Well Wushen-1 is an important deep exploratory well drilled in Dagang Oilfield, with its designed total depth (TD) at 6000m and actually drilled to TD at 5852m in 393 days. It’s the deepest well of onshore oil field in east China, and its drilling is very difficult due to the complicated geological conditions and high geothermal gradients. This well sets two records of onshore oil field in China, i.e., the deepest 311mm diameter hole and the longest running depth of 244.5mm casing. The paper describes the key technologies for casing program optimization, large hole drilling, drill pipe and casing protection, running the 244.5mm casing, under-balanced drilling, cementing and drilling fluid technologies, etc.