This study employed a level set method to establish a two-dimensional finite element model of nanosecond laser to simulate the forming process of titanium alloy micro-pit structure covering heat transfer, fluid flow, surface tension, and Marangoni effect. In a single pulse period, the Marangoni effect caused by the surface tension gradient significantly affects the formation of the crater structure during melting, vaporization, liquid phase migration, and solidification of the material. The formation of sputtered droplets arises from the combined effect of recoil pressure, surface tension, and thermal capillary force on liquid phase migration and sputtering. In the multipulse period, the differential surface tension of the ablation edge in the horizontal and vertical directions causes the height of the crater to increase significantly with the number of ablation; however, the width of the crater does not change significantly. Because the influence of plasma shielding on the incident laser was not considered in the model, it was only suitable for predicting the geometric size of the micro-pits when the number of ablation was less than 15 times.