Natural gas downhole choke process inlet is high temperature and high pressure. Usually it can achieves 10~30MPa, while it will be higher in high pressure drilling well. It is installing thousands of meters underground. It is difficult carrying on field test during working process. These special situations make the choke outlet flow being complex, which includes expansion wave, compression wave, and energy transformation. The physical experiment is difficult. To be more accurately analyzing the compressible viscous turbulent motion of downhole choke internal flow field, this article uses RNG − model for three dimensional numerical simulation. It analyzes the result of flow field streamlines, velocity, Mach number, pressure, and temperature distribution. It analyzes the influence on hydrate formation of choke working process. Numerical calculation can provide useful reference for the prevention of natural gas hydrate formation and optimization design of downhole choke.