The invention discloses a coagulation promoting early strength type polycarboxylic acid water reducing agent for metro shield tunnel segments. The coagulation promoting early strength type polycarboxylic acid water reducing agent is prepared from, by weight, 5-30 parts of water reducing type PCE mother liquor, 10-40parts of coagulation promoting early strength PCE mother liquor, 0.02-0.05part of air entraining agent,0.02-0.05part of defoaming agent, 0.5-5.0part of coagulation promoting agent, 0.01-0.02part of rust inhibitor, 0.01-0.02 part of preservative and a moderate amount of water. Based on a compounding mechanism of a concrete admixture, the water reducing type polycarboxylic acid mother liquor and the coagulation promoting early strength polycarboxylic acid mother liquor serve as main materials, the air-entraining agent, the defoaming agent, the coagulation promoting agent, the rust inhibitor, the preservatives and other components having good compatibility serve as auxiliary materials, a uniform solution is prepared through mixing and stirring, namely proper coagulating time and early strength can be obtained, and accordingly the polycarboxylic acid water reducing agent for the metro shield tunnel segments is obtained.