In　order　to　get　the　dynamic　characteristics　of　air　source　heat　pump　unit　during　the　start-up　and　energy　regulating　processes,　a　dynamic　simulation　model　was　setup.　Moving　boundary　method　was　used　in　the　model　for　the　heat-exchangers.　The　compressor　and　expansion　valve　were　enacted　as　steady-state　components　considering　their　relative　short　time　constant.　The　whole　dynamic　simulation　process　was　put　forward.　The　energy　regulating　strategy　of　the　piston　compressor　was　analyzed　in　detail.　A　typical　dynamic　operating　process　was　chosen　to　validate　the　model.　The　average　error　between　the　simulating　results　and　the　field-testing　results　was　below　10%,　which　indicates　that　the　model　established　in　this　paper　can　be　safely　applied　in　simulating　the　start-up　and　energy　regulating　processes　of　the　air　source　heat　pump　unit.