Abstract: In order to solve the worldwide problem of hull instability due to the puncture by the jack-up drilling platform plugging in "egg shell" formations, engineers in CNOOC innovatively proposed a structure for monitoring and early warning and its operation methods. Aiming at the puncture and the instability of the leg foundation of the jack-up drilling platform in the complex formations in multiple oil fields of South China Sea, CPT test is carried out at the bottom of pile shoe by installing CPT structure on the leg truss of the jack-up drilling platform. The formation parameters including egg shell layer under pile shoe are recorded. Through the stratum parameter processing system, engineers can quantitatively analyze the possibility of the puncture, so as to provide early warning for the possible puncture and make timely adjustments to the in-place plugging operation. The result of numerical simulation shows that the structure and the operation method are reliable and effective, which can accurately monitor and warn the stratum with punctures in theoretical calculation, and effectively avoid the occurrence of punctures. It also plays a positive role in the safe control of plugging and improves the safety of the large offshore equipment.