The invention provides a maleate polycarboxylic type concrete slump retaining agent and a preparation method thereof, and aims to solve the problem that the existing polycarboxylic slump retaining agent has large loss when used in concrete. The maleate polycarboxylic type concrete slump retaining agent has the molecular weight of 8000-15000, and the molecular formula is shown in the description. The preparation method of the maleate polycarboxylic type concrete slump retaining agent comprises the following steps of preparing a maleate mixture through an esterification reaction of maleic anhydride and methanol and preparing the maleate polycarboxylic type concrete slump retaining agent by adopting the maleate mixture, macromonomer TPEG and deionized water through a polymerization reaction.The slump retaining agent and the preparation method thereof, provided by the invention, have the advantages of simple preparation process, simple equipment, polymerization reaction at room temperature and low energy consumption.