Prediction of drought and flood events can be difficult, but the standardized precipitation index (SPI) calculated from monthly data may be a useful tool for predicting future dryness/wetness events in China. The rainy season SPI was calculated from monthly precipitation data from 3804 meteorological stations in China. The spatiotemporal variation, periodic change, and trend in rainy season SPI from 1961 to 2014 in eight regions were investigated. The results indicate that the rainy season SPI is valuable for assessing dryness/wetness spatial and temporal variations. The SPI time series in the northwest and southwest show increasing trends, while northeast China, south China, and Taiwan show more than one upward/downward trend during the study period, and the SPI time series in central, east, and north China show no change in trend. South China has an approximately 10-year periodic oscillation, while the other regions show an approximately 16-year periodic oscillation. The results of this study imply that the SPI can be used to explore historical drought/flood spatiotemporal variations, as well as to predict future wetness/dryness variations.