The　shrinkage-reducing　type　polycarboxylate　superplasticizer　(SRPCA)　has　become　a　hot　research　issue　both　at　home　and　abroad　for　its　perfect　water-reducing　ability,　outstanding　shrinkage-reducing　and　slump　retaining　ability.　The　effect　of　ordinary　polycarboxylate　superplasticizer　(PCA)　and　shrinkage-reducing　PCA　on　the　drying　shrinkage　of　cement　mortar　was　studied　thoroughly　in　this　paper.　The　result　showed　that　the　SRPCA　can　effectively　reduce　the　drying　shrinkage　of　cement　mortar.　Moreover,　the　shrinkage-reducing　mechanism　was　discussed　from　the　aspect　of　molecular　structure　to　the　solution　surface　tension　and　also　mortar　water　retention.　It　indicated　that　the　solution　surface　tension　had　certain　impact　on　the　PCA　shrinking-reducing　ability,　meanwhile　the　perfect　water-retaining　ability　conduce　to　the　shrinking-reducing　improvement.　Besides,　the　introduction　of　shrinking-reducing　functional　groups　to　the　ordinary　PCE　molecular　structure　can　reduce　the　polymer　solution　surface　tension,　control　the　air　content　in　the　concrete　and　decrease　the　drying　shrinkage　of　cement-based　materials.