The effect of polycarboxylate superplasticizer and its content on efflorescence of cement-based decorative mortar was studied. The results show that polycarboxylate superplasticizer can significantly reduce the primary and secondary efflorescence areas of decorative mortar. When the polycarboxylate superplasticizer content is higher than 0.6%， basically no efflorescence occurs in the decorative mortar. After adding superplasticizer， the total porosity， number of surface pores， internal porosity， water absorption of gross pores and connected pores of the decorative mortar decrease， and the surface efflorescence of the decorative mortar is restrained.