Based on daily observation data (temperature, wind, relative humidity and visibility) of five cities and counties in Hainan during 1965 to 2012, the paper develops a New Climate Index for Tourism (NCIT). This index is used to quantitatively evaluate the regional tourism climate resources in Hainan, and investigate the impact of climate change on tourism. It turns out that: 1) The annual frequencies of ideal tourism weather conditions in the five cities and counties all show downward trend with fluctuations; the dominant factor affecting tourism condition in Sanya is wind, and it is apparent temperature in the rest of cities; the seasonal distribution of the frequency of ideal tourism weather condition in Wuzhishan is unimodal, while it is bimodal in other cities. 2) In winter and earlier spring, the climate warming has little influence on the tourism condition of Sanya, but itll obviously improve the tourism climate environment of other places; in summer and early autumn, the tourism condition are generally in disadvantage conditions except in Wuzhishan; for the full-year, climate warming does more harm than good to the tourism comfort degree in Haikou, Sanya and Changjiang. 3) In summer and early autumn, the increase of humidity in Sanya, Qionghai and Changjiang will improve the tourism comfort degree due to the frequency of the rainfall; however the humidity increase in winter will benefit the tourism condition of Wuzhishan. 4) The new climate-resolving index for tourism not only shows the characteristics of tourism climate resources in different parts of Hainan, but also can be used to evaluate the effects of climate change on tourism climate resources. Statistical analysis shows that the tourism climate conditions are closely related to the climate change and geographical environment.