The invention discloses a micro-molecular phosphate dispersing agent. The micro-molecular phosphate dispersing agent is structurally characterized in that as for the structure of the micro-molecular phosphate dispersing agent, one or more amide groups (-CO-NH-) are included, one or more bidentate phosphorous acid groups (-CH(OH)(PO3H2)2) are included at the tail end of the structure, and a polyether segment, an amide group chained polyether segment and a terminal group are further included, wherein the weight-average molecular weight of the polyether segment is 200-5000. The micro-molecular phosphate dispersing agent has good slump loss resistance and can be sucked to surfaces of cement particles faster, thereby being beneficial to achieve the adaptability of an existing water reducing agent to clay. Besides, the micro-molecular phosphate dispersing agent has the cement hydration retarding capacity and is beneficial for summer construction and pumping construction of concrete.