Disadvantages of coal seams in China are of low permeability, low reservoir pressure and low gas saturation, and many researches show that the gas flowing in low permeability media needs a starting pressure gradient. Based on previous researches, a threedimensional, two phases coupled flow mathematical model was presented to describe the characteristic of fluid flow in tight coalbed methane reservoir. Besides, the fully implicit numerical model was given by the finite difference method and linear equations were solved by Orthomin method. Finally, the simulation was conducted by the welltest data of some production wells in Qinshui Basin. The results indicate that the existence of starting pressure gradient makes the depressurization effect worse and delays the coming of the gas production peak under the other conditions. Compared with the production data of this well, the simulation result is reasonable and the model could represent the characteristic of fluids flow in tight coalbed methane reservoirs.