Abstract: In order to solve problem that the jack up rig's penetration depth has a large error between prediction and reality in the process of leg penetration, even punch-through happen. For the reason, a number of leg penetration test completed in the Bohai Sea coastal department to measure stress change around the leg. According to a reasonable plan to cover up soil pressure, fnished study of radial, tangential and vertical variation very well, it provides scientifc basis and guidance for desgin and construction of offshore drilling rig's leg penetration. Tests showed that legs' radial influence to the soil is 3 times of the spudcan's diameter, leg's the vertical influence to the soil is greater than 3 times of the penetration depth.