Taking Fujian Province as the example，the paper focuses on the phenomena of more frequent floods caused by the rainfall during the transitional periods of summer and winter over recent years. Those periods are climatically scarce of rainfall in normal cases. The developing features of precipitation intensity in the past 55 years are analyzed, adopting the composite method so as to explore the connections between the main circulation system of East Asian Monsoon, its regional vapor, convective conditions, and the precipitation intensity during the transitional periods of autumn and winter in Fujian Province. The results show that (1) Both the rainstorm frequency and the precipitation intensity were on an increase, with an abrupt change of precipitation intensity around the year 2010(2) The year with strong (weak) precipitation intensity was featured of a westward (eastward) and stronger (weaker) subtropical high, and the East Asian highaltitude circulation was relatively straight (big meridional variation). Meanwhile, the East Asian Winter Monsoon was weaker (stronger), and the main part of cold air was northward (southward), which is helpful (unhelpful) to the convergence of cold and warm air streams in Fujian. (3) In the year with strong (weak) precipitation intensity, the SW (NE) vapor transportation over Fujian was obviously enhanced, also with the vertical upward movement strengthened (weakened), indicating that the water vapor transportation and convections conditions are both helpful (unhelpful) to the occurrence of heavy rain.