Pipeline transportation of CO2 is the key link to realize carbon capture, utilization, and storage. CO2 pipeline transportation may face the risk of leakage, which poses a great threat to the production process and personnel safety. It is of great significance to study the leakage and diffusion characteristics of CO2 in pipeline transportation for the safety design and personnel protection of the offshore CO2 storage platform. In order to study the leakage and diffusion characteristics of CO2 in pipeline transportation on offshore platforms, a physical model of a target platform and several numerical models were built, and a series of pipeline CO2 leakage and diffusion simulations were carried out using the method of numerical simulation. Based on the simulation results, the temperature distribution and CO2 concentration distribution on the offshore platforms after leakage were measured and analyzed. The influence of leakage direction (horizontal and oblique 45° upward) was also studied. Dangerous areas on the platform and suggestions for staff evacuation were given according to the simulation results. The research results of this work can provide guidance for the safe operation of offshore CO2 storage platforms.