Abstract: Pipeline transportation efficiency and safety are seriously affected by black powder in natural gas pipelines. The black powder removal is less efficient, and the pig blockage phenomenon is easy to occur when using existing pig with leather bowl, magnet and steel brush. The impingement flow field generated by the jet can bring a good removal effect against the liquid accumulation and impurities in the pipeline. Based on the jet principle, a method of cleaning black powder in natural gas pipeline by jet pig was proposed. To obtain the most optimal jet cleaning effect, it is necessary to optimize the key structural parameters of the Venturi nozzle in pig nozzle structure. The Venturi nozzle structure comprises a contraction section, a horizontal section and a diffusion section, wherein the parameters of the diffusion section is crucial to the jet effect. Based on the principle of computational fluid dynamics and the simulation tool Fluent, the actual gas state model was used to define the natural gas parameters in the pipeline. Taking into account the influence of diffusion length and diffusion angle in the diffusion section of Venturi nozzle, the jet process of the pig was simulated and analyzed. By comparing the nephogram and variation curves of the flow rate and turbulence kinetic energy of different diffusion section parameter models in jet flow field, the nozzle structure of gas pipeline jet pig with the optimal jet effect was obtained.