The molecular dynamics method was used to simulate the atomic diffusion behavior of diamond and titanium during the hot pressing diffusion process. The atomic diffusion process at the interface between diamond and titanium at different diffusion temperatures was simulated, and the atomic concentration distribution, diffusion velocity and simulated diffusion coefficient were obtained. The hot pressing diffusion method was used to coat a titanium layer on the diamond surface and the width of the diffusion band at the interface was measured. The research results show that the diffusion speed of C atoms is greater than that of Ti atoms during the diffusion process. With the increase of the diffusion temperature, there exist two stages of atom diffusion, low speed and fast stages. Data fitting of the simulated diffusion coefficients through the molecular dynamics simulation of hot pressing diffusion can be used to determine the diffusion factors and activation energy values of C and Ti atoms. The formula of atomic diffusion coefficient calculation can be determined through a simple and effective method. The calculated value of diamond and titanium diffusion band width is close to the measured value, which indicates that the formula of atom diffusion coefficient obtained by the molecular dynamics method is feasible.