UVGI (Ultraviolet Germicidal Irradiation) system is recently considered for the sterilization of indoor air and practically applied to the buildings where need hygienic control mainly in America and Europe. In this study, the factors influencing the germicidal effect such as UV intensity and exposure time were reviewed and the several methods to evaluate the germicidal efficacy of UR (Upper Room)-UVGI system were introduced. The methods mainly use CFD simulation to calculate UV dose, considering the distribution of UV intensity of UR-UVGI system and the air flow induced by air handling system in a room. The methods were applied to a typical 4-patient ward model. Results showed that the positions of UR-UVGI system and supply or exhaust openings are important for UV dose. For example, spatial average UV dose decrease when UR-UVGI system is installed near the exhaust openings. Similar results were shown in the cases that the contaminants assumed to be exhausted from the mouth of patient. In the cases assuming infectious microbe flow in through supply openings or breathing of occupant, the germicidal efficacy of UR-UVGI could be evaluated with the methods.