In view of the male and female rice being sensitive to the clear and rainy weather in hybrid rice breeding,the continuous overcast or rainy weather that lasting 3 days or more is studied in terms of probability distribution by using the rainfall data (1961 — 1996) of Jianyang city. And the probability of occurance of overcast or rainy weather mentioned above during a period of ten days is also studied similarly. The best period of hybrid rice breeding in Northern Fujian is then settled.