To study the gas transport characteristics in the microchannels of nuclear power plant containment concrete, a micro-scale gas transport model was constructed based on an improved lattice Boltzmann method (LBM), and the effect of Knudsen number (Kn) on the gas transport behavior within the microchannel was analyzed. Firstly, a numerical calculation framework for gas transport was established using the D2Q9 velocity discretization model, and Zou-He boundary conditions were introduced to simulate gas flow characteristics under different pressure environments. Then, based on the Knudsen number, the free molecular motion was controlled, and the velocity distribution, mass flow variation, and pressure gradient characteristics of gas flow within the microchannel at different Knudsen numbers were studied. Finally, the accuracy of the improved LBM model was verified by comparing the results with those from the traditional Navier-Stokes method, and its applicability in microchannel gas transport research was discussed. The results show that as Kn increases, the gas flow in the microchannel exhibits significant slip effects and discontinuity features, which cannot be accurately described by the traditional Navier-Stokes equations. At Kn=0.194 and Kn=0.388, the outlet mass flow of the gas decreased by 15.2% and 28.7%, respectively, indicating that the mean free path of molecules has a significant impact on flow resistance. Moreover, under different pressure conditions, the velocity distribution of the gas flow in the microchannel shows noticeable differences, with more uniform flow at higher pressures. The improved LBM model can effectively simulate the gas transport characteristics at the micro-scale and provide theoretical support for predicting the gas flow behavior within the microchannels of nuclear power plant containment structures.