Abstract: The Morlet wavelet is used to analyse the variation of the runoff series of Changdu，Jiuzhou，Jinghong of Lancang river basin after the vacancy of which had been filled.The dominant periods of the runoff in different hydrologic stations are confirmed，and the periodical variation and fluctuation of rainy season and dry season with multi-scale of time are analysized.The result shows that the runoff in rainy season controls the variation of the runoff of the whole year.There is a dominant period of 14 years in the whole river basin，and the linear trend of the runoff is decreasing slowly.The runoff in the period of 2004~2010 is in the last stage of a high flow period，and another low water period is coming.

摘要： 采用Morlet复小波对澜沧江下游段降水量进行分析，揭示了澜沧江下游地区年度降水量的多尺度振荡特性和周期性变化，确定了主周期。分析结果表明，澜沧江下游河段在24a时间尺度上存在明显的周期性丰、枯变化，其它在12a和36a尺度上的周期性振荡能量较弱，周期变化不明显。根据主周期预测，2004年～2010年该地区处于降水量偏多期的末段，逐步趋于下一个枯水期的到来。