This study is conducted to find out how the heating and cooling loads change by thermal performance by the dynamic heat load simulation program. The study results are as followings. (1) It is revealed that SC is changeable if a window is Low-E coated and by the colors of windows. U-value of window is highly related to the thickness and the kind of window rather than the colors of window. (2) The thermal insulation property of double window whose U-value is distributed 1～2W/㎡K is twice of the thermal insulation property of single window. The mean U-value of PVC window is about 1.0W/㎡K beneficial compared to the mean U-value of aluminum window, which is concluded that it is highly advantageous to take in consideration of the thermal insulation property. (3) As SC decreases by 0.1, it shows that annual heating and cooling loads decrease by approximately 5%. And as U-value of window increases by 0.5W/㎡K, annual cooling and heating loads increase by approximately 15%. (4) The simulation results show that annual air-conditioning and heating load is different by 134% to the utmost, as it is appeared to be minimums of 213 MJ/㎡･yr in case of U-value0.6-SC0.6 and maximum of 499MJ/㎡･yr in case of U-value3.0-SC0.4.