Military activities are one of the important factors affecting the airspace capacity of the terminal area. In order to predict the airspace capacity more accurately, the restricted flight zone is proposed to represent the area affected by military activities, and the corresponding design method is given. Based on the theory of maximum flow and minimum cut, the terminal area capacity affected by military activities is calculated. This paper analyzes the characteristics and defects of traditional algorithms at home and abroad, combines the principle of genetic algorithm, and use the improved genetic algorithm to solve the bottleneck of terminal area capacity affected by military activities. This method effectively avoids the limitation of exponential increase of computation. The corresponding population generation method, encoding and decoding method, fitness calculation method and cross mutation method are designed in the algorithm. The effectiveness and feasibility of this method are proved by an example simulation.