Based on the runoff data at Yingluoxia Stationin Heihe River from 1944 to 2004, the inter-annualchange, intra-annual distribution characteristic, and stability characteristic of mountainous runoff at the station, as well as the impacts of runoff change on regional water resource security, were analyzed.Results showed that (1) runoff took on an increasing trend in the past years,but the trend was not evident. Runoff change was not influenced by human activities sig nificantly and high and low water changes were equivalent.(2) Runoff in flood season (from May to October) was over 80%,so the percentage of run off in other months was small.(3)The runoff variation coefficients of each month in a year were small. The run off var-iation coefficients for January, March, and December were less than that for the whole year,so the stability characteristics w ere good,while those for other months were greater than the whole year.(4)The increase of annual runoff, especially the increase of run off in May and June,added regional water available and relieved Critical Drought.(5) The change of annual runoff was small. The intra-annual distribution characteristic became more and more homogeneous and the rate of high and low water became more and more low.These changes were helpful to develop and utilize water resources of Heihe River.(6)The increase of annual run off, especially the increase of runoff from August to October, w as helpful to enforce the plan of w ater reallocation in the middle reaches.