The invention provides a slump loss resistant agent for concrete with medium and low slump. The slump loss resistant agent for concrete with medium and low slump is a polycarboxylic acid slump loss resistant agent synthesized by using macromonomer acrylic ester, and is prepared by free radical copolymerization reaction of a monomer a, a monomer b and a monomer c, the molar ratio of the monomer a, the monomer b and the monomer c is 1:1-10:2-15, and the monomer b, the monomer c, a used initiator and a used chain transfer agent participate in reaction in a variable-speed dripping mode. The weight-average molecular weight of the slump loss resistant agent is 20,000-70,000. The slump loss resistant agent for concrete with medium and low slump has the excellent effects of low mixing amount, excellent cement adaptability and clay adaptability, stable slump and capability of meeting requirements of the concrete with medium and low slump.