Abstract: Although there is an annual mean precipitation about 1 700 mm in Guangdong Province, it greatly varies with season and region. Flood season (April-September) includes above 80% rainfall of a year, and meanwhile the rainfall has a significant intra-seasonal variability. On the other hand, large evaporation due to high average air temperature also balances some part of the great precipitation in Guangdong. An index to reflect the drought is defined using rainfall and temperature observations of 86 surface stations in Guangdong. The index distinguishes the dry and wet season in Guangdong and reflects the fact that there is a dryer climate in the south than elsewhere of Guangdong in spring and a wetter climate in the north in fall, which indicates the index is reasonable. The trend analyses give an understanding of the linear humidity change. For the whole province of Guangdong, the climates from February to March, from July to August and December tend to be wetter than before, and dryer from October to November and few changes in months else. The results show that the autumn drought would be more severe in the future and the winter-spring drought would be lighter. The spatial distribution of the linear trends has a great difference and its interannual variability is affected by air-sea and air-land interactions.