Water-reducing agent for mortar is a surfactant. It is an additive which can reduce the water demand in mortar blending under the condition that a mortar's consistence or fluidity or workability is kept unchanged.In dry-mixed mortar, commonly used powdered water-reducing agents are based on naphthalene, melamine and polycarboxylate. Among them, polycarboxylate accounts for the most proportion due to its high efficiency and is also called superplasticizer.