Utilizing the runoff and precipitation data during 1960-2009 from Xianyang Station of main stream of Weihe River,and adopting the Mathematical Statistic Methods like Kendall’s rank correlation coefficient,R/S analysis, and M-K mutation test,has analyzed the change trend and mutation characteristics of the seasonal runoff in the mid-stream of Weihe River.Obtained the results as that:(1)The runoff in each season of the midstream of Weihe River all has shown a significant decreasing trend,especially in the fall .And in future,the flow changes will be maintained the same trend that continued decreasing feature;(2)Concentrated period of the average annual flow at the middle reach of the Weihe River was mainly distributed around in mid-August,the concentrated period of annual precipitation was mainly distributed around the end of July .It was probably needed 32 days from rain after stopping storage,overland flow,flow into the river channel,then convergence to the downstream river,Runoff lag period to precipitation was continued to ex-tend .The runoff coefficient has been shown a decrease trend in the past 50 years at the middle reach of the Weihe River;(3)Adopted the M-K mutation test method and the sliping t-test method ,has obtained the mutation point time was 1987,the mutation time was more close in Spring and Autumn,but the summer mutation time was more close to the av-erage annual mutation time .%利用渭河干流咸阳站1960-2009年径流及降水数据，采用Kendall秩相关系数、R/S分析法、M-K突变检验法等数理统计方法，分析了渭河干流中游四季径流变化趋势及突变特征，得出结果：（1）渭河干流中游四季径流均呈极显著递减趋势，尤其是秋季径流减少最为明显，并且未来流量变化与现在保持相同的态势，即有持续递减的特征；（2）渭河干流中游段年均流量的集中期主要分布在8月中旬左右，年降水量集中期主要分布在7月底左右，径流从降水开始经过停蓄、漫流、河槽集流，然后汇流至下游河道大概需要32 d左右的时间，径流对降水的滞后期在不断延长，50年来渭河干流中游径流系数呈下降趋势；（3）采用M-K突变检验法和滑动 t检验法得出年均流量的突变时间点为1987年，春季与秋季突变时间一致，夏季突变时间与年均突变时间较为接近。
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