Abstract: To analyze the variation characteristics of flood and drought in Altay,Xinjiang,China,the flood and drought index(i.e.,W index) was calculated with the precipitation data at seven stations during 1961-2008 mainly using the linear trend method and Mann-Kendall method(M-K method for short).By selecting NCEP/NCAR data from five typical flood and drought years,the characteristics of 500hPa circulating situations and the correlation between the W index and 500hPa circulating data of previous year were analyzed.The results showed that the W index data had fluctuation with years and seasons,and exhibited the alternation from droughts to floods,continuous floods or droughts.The results of M-K mutation test showed that the inter-annual W index mutation mainly happened in the middle and later periods of 1960s and the middle of 1980s.By analyzing the 500hPa anomaly fields of typical flood and drought years,it was shown that the Eastern Europe to Western Siberia had a high positive anomaly in drought years,whereas,Xinjiang was controlled by warm ridge,of which were on the contrary in flood years.If the polar vortex area was small and the strength was weak in the past year,and the Western Pacific subtropical high-pressure was stronger and the area was big,together with zonal circulation,the W index was trend to be bigger than normal in the next year,which means that it was possibly a flood year.The scientific study of the flood/drought rules in the region,the timely adjustment of agricultural structure,and reasonable arrangements for agricultural production,were effective measure to defend flood/drought and reap a bumper harvest.

Key words: Flood and drought index(W index), Flood and drought index(W index), Linear trend, Mutation test, Circulation feature