To research indoor air pollution in the training rooms of technical high school, the temperature, air current, humidity, CO₂, CO, O₃ were measured by Indoor Climate System(ICS 500, Casella, UK) at each classroom, scientific laboratory, electricity training room, electronic equipment training room and welding training room. The change of air pollution concentration and its correlation were additionally compared and analyzed. At closed small space such as classroom, scientific laboratory, electronic equipment training room and electricity training room, the CO₂ concentration was obtained to the 2,030ppm(max.), which is higher than notified and recommended standard value(1,000ppm) by Ministry of Health and Welfare and Ministry of Environment, Korea. At welding training room where is larger and more ventilated than general classroom, CO concentration was measured to the 3.6ppm, which is higher than average 1ppm measured at other training rooms. The concentration of O₃ is not yet regulated from the standards of underground air quality, but at welding training room it was measured as 0.11ppm(max.) that is higher than 0.01ppm measured at other training rooms. The higher value of temperature, air current, radiant temperature and CO₂ concentration was shown at scientific laboratory, electricity training room and electronic equipment training room where are closed and same with the scale of classroom. And the higher concentration of CO₂, CO and O₃ was shown at welding training room which was opened larger classroom. The indoor air pollution by CO₂, CO and O₃ may directly affect on the training room where many students work at a small space, and they should be controlled appropriately. Each experimental formulas were made for the estimation of CO₂, CO and O₃ concentration depending on some kinds of variables at each training room. It is found that indirect ventilation system with a filter will be needed for regular and constant ventilation and the ventilation system should be applied to protect and make clean and comfortable environment of training rooms at technical high school.