Hexamethylene dicarbamate (HDI) is an important aliphatic isocyanate are often used in aerospace, aviation, and polymer materials. Compared with aromatic isocyanates, HDI does not contain a benzene ring and has a symmetrical carbon chain skeleton, which makes it light stable and highly decorated. Studies have shown that the non-phosgene method can be used to prepare HDI through the thermal decomposition of the key intermediate hexamethylene dicarbamate. In this work, 1,6-hexanediamine (HDA) and diethyl carbonate (DEC) are used to synthesis hexamethylene dicarbamate ethyl ester (HDEC) under the catalysis of manganese acetate anhydrous. The structure and purity of the self-made HDEC standard sample are determined by FT-IR, 1H-NMR and TG, and a quantitative analysis method is established. Furthermore, qualitative analysis of the main and side products of the reaction is carried out by GC-MS, and the reaction pathway is inferred. At the same time, the reaction parameters are optimized and the reaction mechanism is speculated. The results show that the reaction is achieved in two steps. First, HDA reacts with DEC to form a monosubstituted 1-(6-amino)-hexamethylene monocarbamate (HMEC) intermediate, the process is that manganese acetate attacks -NH2 at one end of HDA to form reactive intermediate I [H2N(CH2)6NHCOCH3], and reactive intermediate I reacts with DEC to form HMEC. Second, HMEC further reacts with DEC to form HDEC target product, the process is that manganese acetate attacks -NH2 at the end of HMEC to form reactive intermediate II [CH3CH2COONH(CH2)6NHCOCH3], and reactive intermediate (II) reacts with DEC to form HDEC. The CH3COOCH2CH3 reacts with Mn(OH)2 to form manganese acetate catalyst in the reaction process. In addition, DEC reacts with HDA and HMEC to form urea by-products during the reaction. Under the optimum reaction conditions, the molar ratio of DEC to HDA is 3.5:1, the reaction temperature is 120℃, the amount of anhydrous manganese acetate catalyst is 15% of HAD initial amount, the reaction time is 5 h and the rotating speed is 400 r/min, the conversion of HDA is 100% and the yield of HDEC is 89.6%.