Abstract: The linear warming trend over the last 50 years (0.13 ℃ per decade) is nearly twice that for the last 100 years, and during 1995-2006 rank among the 12 warmest years in the instrumental record of global surface temperature since 1850 (IPCC AR4, 2007). Lots of researches denote that heat wave could lead to heat stoke and even death, so it has become a meteorological disaster that deserves attention from every government. In order to reduce the impact of heat wave on human health, lots of indices for thermal comfort forecast have been established both at home and abroad. However, atmospheric pressure and solar radiation are seldom recognized as factors influencing comfort, especially in China. In order to establish a Universal Thermal Climate Index (UTCI) including all meteorological factors that influence thermal comfort and human comfort in summer, an extensive questionnaire survey concerning the comfortable conditions is conducted. The database consists of questionnaire filled by 205 students those are participating in military training from 06:00 to 20:00 outdoor from 21 to 25 August 2009. Thermal sensations are reported on a five point scale and extensive statistical treatment of the data is performed. A multivariate analysis scheme is developed to handle the bulk of the data and ensure the validity of the results. The weather parameters are observed by NUSIT Weather Station being 500 meters away from the investigation site. The study confirms a strong relationship between thermal comfort and microclimatic conditions, including solar radiation, air pressure, maximum temperature, wind speed and relative humidity, ranked by importance. Therefore, the influences of atmospheric pressure and solar radiation have to be considered when forecasting the thermal comfort. UTCI is improved and formulated according to the body feeling temperature index of International Society of Biometeorology and current formula at home. The relationships between thermal comfort according to questionnaire surveys and indices including single element, bivariate, three major elements and UTCI are established and compared based on the database of questionnaire survey. The results show that domestic indices needs improving. The forecast effect of new UTCI adding atmospheric pressure and solar radiation is better than other indices both at home and abroad. Above all, based on weather forecast numerical model and SolAlt solar radiation model, the improved UTCI is an applicable index of thermal comfort forecast in Nanjing and it will provide better public weather servic