The thermal stability of hydrogen-containing DLC coating is poor, and the work aims to explore the microstructure changes of hydrogen-containing DLC coating at high temperature and their impact on mechanical properties. The hydrogen-containing DLC composite coating with Si as the transitional layer was deposited on the surface of S136 stainless steel by plasma enhanced chemical vapor deposition (PECVD). The microstructure of DLC coating was investigated by optical/scanning electron microscopy, Raman spectroscopy, XPS (X-ray photoelectron spectroscopy) and three-dimensional profiler, the mechanical properties of DLC coating were studied by scratch, reciprocating friction wear and nano-indentation experiment, and the nano-indentation experiment behavior of DLC coating was simulated by LAMMPS to analyze the microstructure characteristics in annealing. The coating was subject to annealing conditions of 400 ℃ for 2 hours and 600 ℃ for 2 hours. Under the former condition, Raman spectroscopy showed an increase in the intensity ratio of the ID/IG peaks from 0.7 to 1.5, indicating graphitization transition, accompanied by a decrease in baseline slope and H element segregation. XPS analysis revealed an increase in sp2 hybridization and oxygen content in the coating under this condition, as well as an increase in surface roughness. At 600 ℃, severe oxidation of the DLC coating was observed. Under that condition, the matrix stainless steel was also oxidized. Molecular dynamics simulations using LAMMPS suggested a decrease in molecular bond length at 400 ℃ high temperature. The three-dimensional profile test showed that the roughness under the unannealed condition was mainly from the large particles produced during deposition. At 400 ℃ for 2 h, the coating had the minimum surface roughness. At this time, some large particles in the coating structure fell off, and the coating was basically completely damaged at 600 ℃ for 2 h. The roughness was mainly from the original stainless steel roughness. The scratch test showed that under the condition of 400 ℃ for 2 h, due to the release of the internal stress of the coating and the tighter bonding of the transition layer, the coating had the best bonding effect with the substrate and was the least likely to fall off. The statistical results of LAMMPS simulation showed that the chemical bonds of the original DLC model tended to become shorter after annealing at high temperature. Relative to the unannealed DLC coating, the mechanical properties of DLC coating were best under 400 ℃ for 2 h. Under this condition, the precipitation of mixed H elements in the coating led to the transformation of the original C—H sp3 structure, which occupied a large space to the smaller C—C sp3 and C—C sp2 structure, releasing internal stress in the coating, while ensuring the strength. The nano-indentation experiments showed that the elastic recovery and hardness of the coating were the highest at 400 ℃ for 2 h, compared with that at other annealing temperature. The structure of the DLC coating containing hydrogen changed due to the precipitation of H element at 400 ℃. On the one hand, the coating structure changed from sp3 to sp2 due to high temperature, and on the other hand, the precipitation of H element changed the original C—H sp3 to C—C sp3, reducing the internal stress of the coating and improving the mechanical properties. The coating is basically damaged at 600 ℃ for 2 h, but the substrate still retains part of the coating. This is because the transition layer Si reacts with the coating to improve the heat resistance of the remaining coating. Molecular dynamics simulations using LAMMPS showed that the coating undergoes a graphitization transition at high temperature, leading to a reduction in its hardness.