In order to study the forming mechanism of molten pool and heat-affected zone in the preparation of amorphous alloys by laser additive manufacturing, finite element software ANSYS was used. The thermal effect of laser rapid melting Zr65Al7.5Ni10Cu17.5 amorphous alloy was numerically simulated and analyzed. The simulation results show that, average cooling rate of molten pool is 6.3×104K/s when laser solidification is carried out at single point. Average cooling rate in heat affected zone is 1.4×104K/s, much higher than 1.5K/s of critical cooling rate of Zr65Al7.5Ni10Cu17.5 amorphous alloy. The thermal change of single-point laser melting meets the growth conditions of amorphous alloys. In the process of single-channel laser melting, average cooling rate of molten pool is 2.11×102K/s, still relatively high. However, average cooling rate of heat affected zone is 74K/s and low. In addition, relaxation accumulation occurs in the heat-affected zone. It may cause a certain degree of crystallization. This study provides theoretical basis for thermal effect of amorphous alloys prepared by laser additive manufacturing.