Based on annual precipitation data of long series rainfall stations,this paper uses the mathematic statistics method to study yearly variation of annual precipitation and sequence representation of short series an-nual precipitation,such as1956-2000,1956-1979,1971-2000,1980-2000year,etc.This provides basis for rational selection of a series of hydrology and is significant in investigation and appraisement and synthetic plan of water resources;the result may be applied to the industrial and agricultural production.