In order to analyze the interaction between ultrafast pulsed laser and 4H-SiC at atomic scale, the picosecond laser ablation process of 4H-SiC was simulated by molecular dynamics method of the two-temperature model, and the melting temperature, temperature field, atomic trajectory and ablation region of 4H-SiC were analyzed by different laser energy intensities. The results show that the interaction between picosecond laser and 4H-SiC is mainly thermal ablation, and the ablation process will be intense only after the end of the laser pulse, and the ablation process is more intense and the ablation region is more irregular with the laser energy intensity. The melting temperature of 4H-SiC crystal lattice is related to the system pressure. When the system pressure is 6.1 GPa, the melting temperature of the crystal lattice is 3230 K, which is about 400 K higher than the melting temperature of 2827 K under normal pressure, and the higher the system pressure, the higher the temperature required for the crystal lattice melting. This result provides a theoretical reference for picosecond laser for stealth dicing of 4H-SiC.