In order to study the influence of laser power on the formation of laser-metal inert-gas composite welding seam of ship steel, joint test of 7mm AH36 ship steel plate with different laser powers, microstructure observation and mechanical properties test were carried out. Theoretical analysis and experimental verification were carried out. The optimum technological parameters of weld forming, microstructures and mechanical properties of different regions of weld joints were obtained. The results show that, at laser power of 6kW, current of 220A and welding rate of 1.2m/min, weld forming is the best. The structure of weld zone is lath martensite and a little ferrite. Its tensile strength is 545MPa. The mechanical properties meet the requirements of national standards and China Classification Society specifications. This has certain guiding significance for laser hybrid welding of ship steel.