The invention relates to a hydroxy-terminated organic nitrogen-containing ester and a preparation method thereof. The method comprises the following steps: carrying out reaction on side-group nitrogen-containing dicarboxylic acid and pentaerythritol to obtain carboxy-terminated DAPER, carrying out reaction on organic nitrogen-containing dicarboxylic acid and dibasic alcohol to obtain hydroxy-terminated DADA, and finally, carrying out reaction on the DAPER and DADA to obtain the final product. The preparation method is based on the reaction activity difference among reactant polyfunctional groups, and the finally prepared hydroxy-terminated organic nitrogen-containing ester overcomes the defects of single function, environment pollution in the preparation process and the like caused by difficulty in storage and use and simple structure in the traditional liquid ester. The final product is the high-molecular-weight solid ester, and the terminal group of the molecule is hydroxy; and the hydroxy-terminated organic nitrogen-containing ester contains 12.47-13.76 wt% of nitrogen, and has the advantages of high heat stability, wide applicability and the like.