The invention relates to a platelet preserving agent, which has the following constituents (by weight percent): dipotassium EDTA: 10-14%, sodium citrate: 6-10%, Novocain:0.45-0.55%, Polyvinylpyrrolidone: 0.46-0.50%, polyethyleneglycol 6000: 0.48-0.52%, adenosine triphosphate: 0.03-0.07%, heparan: 0.005-0.015%, prostacyclin: 0.005-0.015%, urokinase: 0.01-0.03%, plasmin: 0.005-0.015%, adrenomedullin: 0.01-0.03%, hydroxyethyl cellulose sodium: 0.15-0.25%, JNSO-2000 long-acting antimicrobial agent: 0.05-0.15%, and water: the residual amount. The platelet preserving agent preparation method provided by the invention has the following steps in sequence: proportioning main raw materials and performing ultrasonic wave action, adding protein material liable to lose the activity and uniformly mixing, performing suction filtration and preparing. The platelet preserving agent provided by the invention enables platelets to maintain the stable state of individual distribution within 24 hours after leaving the body and have no statistical variation within 24 hours, thereby ensuring the accuracy in blood cell analysis. The platelet preserving agent preparation method provided by the invention has the remarkable implementation effect contrasted and verified by testing.