Aiming at the technical problem of poor cementing quality of offshore gas wells with narrow pressure window， the goal of safe and efficient cementing is achieved through the application of light drilling fluid to optimize the slurry column structure and the application of annular backpressure. Three key technical requirements are considered in this paper： the annular backpressure value during the pump stopping process should not exceed 5MPa， the turbulent contact time of the flushing fluid should be greater than 10 minutes， and the wellbore should be self-stable after cementing ending. Then the optimized slurry column structure and the calculated wellbore equivalent cycle density （ECD） with managed pressure cementing （MPC） technology were conducted by which a design method of cementing slurry column structure of MPC for offshore gas wells with narrow pressure window was formed. Taking a high-temperature and high-pressure well in Ledong 10-1 Gas Field as an example， the cementing slurry column structure was optimized， and the wellbore ECD and turbulent contact time was simulated during the entire MPC process. The results indicate that： the requirements of turbulent contact time greater than 10 minutes and leakproof pressure stability can be achieved under the following three conditions： the volume of light drilling fluid is 14~50m³ and the density is 1.822~2.142g/cm³， the volume of the pad fluid is greater than 13m³ and the density is 2.36~2.45g/cm³ and the density of cement slurry is 2.4~2.51g/cm³. The goal of improving the efficiency of cementing displacement and safety construction is feasible with this method.