Abstract: In order to obtain the gas migration laws in the goaf, taking the experimental platform for gas migration in small goaf as the research object, then using computational fluid dynamics software Ansys-fluent, the numerical simulation of gas migration at fully mechanized caving face was carried out; the study is about when U-type ventilation is used in the goaf, the influence of ventilation quantity, high temperature source and sealing respectively on the gas concentration distribution in goaf. The results show that the increase of ventilation rate can obviously reduce the gas concentration in the shallow part of the mined out area; when there is a high temperature in the goaf, with the increasing of temperature, the bottom gas is heated, and the rise of the gas is obvious, which makes the gas accumulation in the upper part of the goaf, after sealing, the shallow gas concentration increased rapidly in the goaf, and the concentration gradient in each direction gradually disappeared, the gas concentration in the whole goaf increased gradually and finally tended to balance.