Cadmium zinc telluride (CZT) is an important substrate material for mercury cadmium telluride (MCT) infrared focal plane array devices. There is a strong exothermic phenomenon during the synthesis of CZT polycrystal. Therefore, controlling the heat release is the basic condition for the smooth progress of the CZT polycrystal material synthesis process. The exothermic intensity and rate of the synthesis reaction can be effectively controlled by changing the initial tilt angle, and a large tilt angle is beneficial to obtain a slow and stable process. Based on the experimental results and thermodynamic analysis, it is shown that the synthesis reaction can be divided into two stages, including liquid-solid phase reaction and liquid-liquid phase reaction between Cd and Te. Meanwhile, the experimental results show that the amount of heat released from the synthesis reaction determines whether the second reaction will occur at high temperatures. Finally, the related mechanism of the secondary reaction is analyzed.