Abstract: In the case of plug discharge,the characteristic of turbulence was studied firstly,then 3-D RNG κ-ε mathematical model was established and verified properly by physical model test data.Based on the computational results of the model,minimum pressure coefficient of plug flow was analyzed and generalized, showing that it appeared double peaks around the sudden-shrink area and the sudden-expand area.When other coefficients are definite the minimum pressure coefficient of the double peak areas decreased respectively when the relative plug length increased,and it decreased sharply when the ratio of plug radius to tunnel radius increased.Besides,it was influenced more by variety of the ratio of plug radius to tunnel radius than that of relative plug length.