The airport gate assignment problem is conventionally modeled as an integer programming problem and is heuristically solved for real-world cases. Recently, it had been formulated as a multicommdity flow problem. However, a real-time algorithm is needed. In this paper, we make use of the time-space network to formulate it as a minimum cost flow problem with side contraints, a set of flow equality constraints. Fruthermore, integer solutions can be obtained at the first phase without branching with the branch-and -bound algorithm in our case studies. The experimental result shows that our model is promising.