The invention relates to an organic nitrogen-containing ester compound taking a carboxylic group as a terminal group and a preparation method thereof. The preparation method comprises the following steps: firstly, taking dicarboxylic acid with a side group containing nitrogen, and pentaerythritol to react to prepare DAPER taking carboxyl as the terminal group; taking organic nitrogen-containing dicarboxylic acid, and dibasic alcohol to react to prepare DADA with the carboxylic group at one and the carboxyl at the other end; finally, taking the DAPER and the DADA to react to obtain a final product. According to the preparation method provided by the invention, the organic nitrogen-containing ester compound taking the carboxylic group as the terminal group is finally prepared based on the difference of multifunctional group reaction activity of reactants, and the disadvantages that a traditional liquid ester compound is difficult to store and use, the structure is simple so that the usage is single, the environment is polluted by a preparation process and the like are overcome; the organic nitrogen-containing ester compound taking the carboxylic group as the terminal group is a solid-state ester compound with high molecular weight and the terminal group of a molecule is the carboxylic group and internally contains 12.02 weight percent to 13.21 weight percent of a nitrogen element; the organic nitrogen-containing ester compound has the advantages of high heat stability, wide application and the like.