Taiwan Environmental Protection Administration (TEPA) has proposed an air pollution cap strategy in order to improve the air quality in southern Taiwan. All large emission sources are involved in this program. There are three fossil-fuel power plants operated by a company in the air basin. The capacity of each plant is 4,320 MW, 2,400 MW, and 1,120 MW. Air pollutant emissions of these three plants were 25,730 ton/year (NOx) and 15,130 ton/year (SOx), respectively. This study discusses control scenarios for these three power plants as a system cap. Air quality modeling work, ISCST3 and Taiwan Air Quality Model (TAQM), also had been conducted to evaluate the effectiveness of air quality improvement. Thirteen control measures were designed for NOx and SOx emission reduction allocation among the three power plants. The results indicated that the measures of "seasonal operation mode" and "bubble control" are the best two for the system. The simulation results of air quality improvement showed that the season-allocation measure may reduce NOx, SOx, and ozone emission levels in episode season. However, the annual emission level showed no significant improvement in other seasons. Implementing the bubble measure for the three power plants resulted in a slight air quality improvement for NOx, SOx and ozone pollution levels in the air basin according to the air quality simulation models. Thus, the bubble measure seems to be the better strategy for the three fossil-fuel power plants.