Abstract: Thermal fatigue crack is the main failure mode of aluminum alloy die-casting dies. According to the phenomenon, an attempt to harden the working surface of die-casting dies with biomimetic units was made by using biomimetic coupled laser welding with filler wire process and laser remelting process, respectively. The propagation of thermal fatigue crack was analysed under different treatments. The ways to improve die service life was explored. The samples of this experiment was processed by Nd:YAG laser.The thermal fatigue cracks were measured or observed at intervals of 500 cycles and the morphology of thermal fatigue cracks was obtained after 5 000 cycles. The experimental results show that the microhardness of biomimetic units that was made by laser welding with filler wire is slightly above the biomimetic units that was made by laser remelting process, samples that is processed by laser welding with filler wire have better thermal fatigue resistance ability.