Aiming at the complex process of separating moisture from natural gas, the gas mixture can be only to separate the water and the hydrocarbon by the throttling effect to make the temperature exceed the dew point, and the accuracy of the parameter identification and analysis of the throttling device will directly influence the separation performance. Therefore, the flow model through the throttle gas is established under the condition of high pressure by the SaintVenantWantzel equation with critical state, which also takes into account the flow condition that the air flow smoothly when the gas flow passes through the throttle valve. Meanwhile, based on the interconnection control between “the value of the crosssectional area/flow temperature of the throttle valve” and the “the value of the crosssectional area/ flow rate of the throttle valve” in the channel, the nonlinear characteristic between the crosssectional area value of the throttle valve and the flow rate and the temperature of the lower section of the humidity LTS is studied. The limit condition of the gaswater separation under this condition is defined. Finally, the static model of the throttle device under the subcritical state is established. By using the commercial software ANSYS, the simulation results verify the validity of the proposed model for throttle valve parameter identification and restrictive condition analysis. Compared with the other two methods, the proposed model has higher parameter identification rate.