All main structure of jacket platforms that have been built and put into operation in China use high strength steel of 355MPa at present. In order to reduce weight to meet the capacity of launching barge， some deepwater jacket under constrcution uses more than 20000t extra-high strength steel of 420MPa， which is produced in domestic. To ensure the securely construction of the jacket， the lamellar tearing performance and susceptibility of domestic extra-high strength steel API 2Y-60 for deepwater jacket are evaluated in this paper through chemical composition analysis， Z-direction tensile test and Z-type window test. The test results mean that the domestic API 2Y-60 steel has good lamellar tearing resistance， which is the basic condition of steels used in jacket tubular joints. The research results can ensure the safety of jacket platform， and also provide a reference for the first application demonstration of similar structural steel.