To　investigate　external　causes　of　motivating　earthquake　on　Wenchaun　in　Sichuan　province,　P.R.C,　the　relationships　between　the　Wenchuan　earthquake,　in　Sichuan　province,　P.R.C,　and　impoundage　in　Three　Gorges　reservoir　were　presented　for　discussion　in　this　paper.　The　relationships　included:　Distance　and　geometry　mode　between　the　Longmenshan　fault　and　the　center　of　gravity　of　large　impoundage　capacity　in　Three　Gorges　reservoir,　effects　of　large　impoundage　capacity　in　Three　Gorges　reservoir,　the　acting　result　of　westward　horizontal　thrust　transmitting　through　hard　and　integral　plate　of　Sichuan　Basin,　time　factor　between　strong　tectonic　earthquake　and　impoundage　elevation.