Abstract: The ability to forecast the timing of florescence in trees is valuable for fruit trees, beekeeping, gardens and tourism. In this paper, measurements of bud morphometry (length and width) of Prunus sargentii were taken when its buds were beginning to expand at Yuyuantan Park in Beijing from 1998 to 2000. Our results showed that linear and exponential equations could adequately forecast the timing of bud florescence. A three-day running mean method measured on three trees was used in the forecast model. The forecast accuracy within 3 days in 2002 was more than 80% of florescence, and the forecast in 2003 was more precise, from 1.6 to 2.1 days. It was found that this new method is a convenient and precise method for forecasting florescence of plants having bigger buds in winter. A primary forecasting model could be developed by amending and perfecting this method by, for example, measuring several trees in a year. Additionally, the method can be applied to forecasting the first day of leaf out.