The objectives of this study were to evaluate the air quality surrounding an indoor swimming pool, to estimate the cancer risk based on the airborne exposure to trihalomethanes (THMs), and to examine the ventilation efficiency by Computational Fluid Dynamics (CFD). Chlorine and THMs were measured poolside, and in the staff room and reception area. The indoor swimming pool was modeled using the Airpak program, with ventilation drawings and actual survey data. Temperature, flow and mean age of the air were analyzed. Levels of chlorine poolside, and in the staff room, and reception area were $203;{mu}g/m^3$, $5;{mu}g/m^3$, and $10;{mu}g/m^3$, respectively. Chloroform was the dominant THM in all sampling sites and mean concentrations were $16.30;{mu}g/m^3$, $0.51;{mu}g/m^3$, and $0.06;{mu}g/m^3$ poolside, in the staff room and reception area, respectively. Bromodichloromethane and Dibromochloromethane levels were respectively estimated as $10.3;{mu}g/m^3$ and $1.7;{mu}g/m^3$ poolside, $1.3;{mu}g/m^3$ and $0.1;{mu}g/m^3$ in the staff room, and were not detected in the reception area. The cancer risks from inhalation exposure to THMs were estimated between $3.37{ imes}10^{-7}$ and $1.84{ imes}10^{-5}$. A short circulation phenomenon was observed from the supply air vents to the exhaust air vents located in the ceiling. A high temperature layer was formed within one meter of the ceiling, and a low temperature layer was formed under this layer due to the low velocity and high temperature of the supply air, and the improper locations of the supply air vents and exhaust air vents. The stagnation was evident at the above adult pool and the mean age of the air was 22 minutes. Disinfection by-products in the indoor swimming pool were present in higher concentrations than in the outdoor air. In order to increase the removal of pollutants, adjustment was required of the supply air volume and the supply/exhaust position.