The　effect　of　aluminium　sulfate　on　cement　properties　was　studied　systematically　and　the　mechanism　was　analyzed　using　XRD　and　SEM　tests.　Experimental　results　showed　that　the　addition　of　aluminium　sulfate　will　shorten　the　setting　time　of　cement,　increase　the　drying　shrinkage　and　improve　the　early　strength;　however　it　will　weaken　the　late　strength　of　cement　and　reduce　the　fluidity.　Micro-research　showed　that　the　addition　of　aluminium　sulfate　will　change　the　morphology　and　location　of　aluminium　sulfate　distinctly.