For health concerns, the residential and commercial heating, ventilating and air conditioning (HVAC) marketplace has become increasingly interested in utilizing ultraviolet germicidal irradiation (UVGI) lights to improve indoor air quality (IAQ). The UVGI technology is a non-chemical and cost-effective approach to disinfection. It can deactivate the DNA of bacteria, viruses and other pathogens and thus destroys their ability to multiply and cause disease. This paper gives the basic conception, design parameters (including air temperature, relative humidity, velocity, duct configuration and lamp intensity, microbial response etc.) and method of UVGI technology in HVAC system to improve the IAQ.