A deep-water jacket widely uses domestic extra high strength steel API 2Y-60 in the design and construction for the first time in China to reduce weight. To ensure the welding quality of the jacket， the heat input of flux cored arc welding with gas shielding （FCAW-G） of extra high strength steel is studied， and the upper， middle and lower limit conditions of heat input are set for welding and testing. Steel plate and corresponding filler metals used for the construction of the jacket are welded. The macrostructure and microstructure of the weld metal and heat-affected zone are analyzed. Tensile， bending， impact and hardness tests are carried out on the weld joints， and tensile tests are performed on the weld metal. The results indicate that the microstructure of the joints becomes gradually coarser with the increase of heat input. The mechanical properties of the FCAW-G joints all meet the requirement of the project. Heat input has a great influence on the strength and hardness of the joints， while has no obvious influence on the impact properties. In order to ensure the properties of the FCAW-G joints， welding beyond the specified heat input should be avoided in the construction of the jacket.