In order to improve the quality of underwater wet laser welding, a self-designed flux were successfully applied to the work of underwater wet welding 5mm thick 0Cr25Ni6Mo3N duplex stainless steel which existed at the 6mm depth in simulated seawater by laser beam. After welding, the microstructure of the top, middle, bottom weld and heat-affected zone of the welded joint was observed by metallographic microscope, and the mechanism of microstructure evolution was deduced. The austenite phase ratio in each area of ??the welded joint was calculated, and we have found that the austenite in most areas is significantly reduced, which deviates from the balance value of the base metal. The reason for this problem is analyzed in combination with the microstructure and morphology characteristics of each area. Positive suggestions are given to promote the growth of austenite and maintain the balance of phases. After the experiment, the failure analysis of the tensile fracture type and friction and wear behavior of the weld was carried out. The average tensile strength of the sample is 810.7MPa, which is 95.3% of the tensile strength of base metal and the average elongation of these samples is 34.4%. The microstructure of the fracture shows obvious cleavage step and some dimples, which belongs to the mixed fracture type. The friction coefficient of the weld is about 0.557, and the friction reduction is better than that of the base metal. The wear failure mechanism is three-body abrasive wear.