Abstract: There is a lack of an evaluation index which can assess the appearance of welds user-friendly and accurately in underwater wet welding. To solve this problem, the weld reinforcement variation coefficient is proposed to be used for evaluating the welding quality. The evaluation index has many advantages such as objective, quantitative, less step and easy operation, which is suitable for popularization and application in practical engineering production. The weld reinforcement variation coefficient grows higher with the worse the uniformity of weld appearance and the lower the welding quality and vice versa. According to the influence of pulse current on the stability of welding process, welding was carried out under different pulse frequency conditions. In view of the influence of wire feeding method on welding process, the stability of underwater wet flux-cored wire welding process was studied by analyzing the wire feeding method with the coefficient of variation of residual high welding seam. The experimental results show that the evaluation results of the index have high consistency with welding quality. The influences of the welding process on the weld reinforcement variation coefficient are analyzed using an X-ray transmission method. The reliability of the weld reinforcement variation coefficient is further verified by researching the welding electrical signal and droplet transfer.