If the difference of the workload in a sector is too big, the airspace capacity will be limited, which will adversely affect the flight safety and airspace utilization. In order to improve the sector capacity, relieve air traffic pressure, the method of the Xi’an terminal sector capacity evaluation and optimization base on controller workload is constructed. Measuring the controller workload by the statistical analysis of the radar data, the comprehensive value of the controller workload, which accords with the Xi’an terminal workload, can be calculated. Then the Voronoi diagram is founded using computational geometry. According to the principle of balanced sector load regulation, and some actual constraints, applying genetic algorithm in terminal control airspace, the optimal design of sector structure can be achieved. Through sector optimization, the capacity of the terminal area of Xi’an is enhanced, the sectors of the control load is balanced, and good results are achieved. 