This　paper　presents　a　new　order-selection　algorithm　for　exponentially　damped　sinusoids　model　based　on　subspace　and　structured　total　least　norm　method.　It　constructs　model　order　estimation　criterion　by　utilizing　the　shift　invariance　of　the　signal　subspace,　and　the　principle　of　total　error　reaching　minimum　when　order　matching　with　the　number　of　signal　components.　The　results　of　simulation　show　a　higher　estimation　accuracy　of　the　new　algorithm.　The　algorithm　is　not　required　to　set　a　threshold　and　penalization　terms,　and　can　accomplish　estimation　procedure　automatically.　It　can　be　applied　to　the　high　resolution　harmonic　retrieval　algorithms.