Abstract: This paper presents a month-seasonly climatic indices of dryness and wetness, and applied to the analysis of periods of dryness and wetness in Guangdong.The results show that, the period from April to September is the wet period, the period from November to January in next year is the dry period. February and March are the transitory period between dry and wet. The wet period is longer than the dry one.The change of period of dryness and wetness is marked by the movement of latitude direction from north forward to south. In the period of March and April, the north region is wet and south's is dry. In the period of September, the pattern is just opposite. The time of transform of dryness and wetness period agrees with that of natural period.This work has an actul value for guiding agricalture products and has an important significance for the research of climatic anomaly.