Abstract: The observational data of phenology and environment during physiological drop phase of Wenzhou citrus in May of 1986 and 1987 are used to analyze both the dynamic feature of blossom drop and premature drop of citrus and the conditions of ecological environment of citrus orchards,such as topography,climate,soil and vegetation. The dynamic trends of the summation percentage of blossom drop and premature drop of citrus are simulated by means of the Logistic theory curve. It is revealed that the differences of dynamic features of blossom drop and premature drop of citrus between the normal year 1987 and the abnormal year 1986.The differences of weather-climate in the middle ten days of May between 1986 and 1987 are compared and analyzed. The results show that the middle period of the middle ten days of May is the peak period of blossom drop and premature drop of citrus.In the middle the days of May 1986,the rapid physiological premature drop and the sharp increase of drop amount were caused by high temperature and low moisture.Therefore,the proper agrotechnical measures taken in time according to the weather conditions during the middle ten days of May is an important link to strengthen the management of citrus orchards. An empiric model obtained based on the Logistic theory model and by the amendment of ecological environment factors(temperature and moisture)have improved simulation effect.It can be applied to predict the dynamics of blossom drop and premature drop of citrus in that year,in order to take necessary measures in a critical moment.