Abstract: To solve the problem of accurate temperature field prediction inside concrete before construction so as to take appropriate construction measures to prevent the thermal cracking of concrete, a sigmoidal hydration heat model was proposed based on the characteristics of cement hydration in this paper. By means of the secondary development of finite-element (FE) software ABAQUS, a 3D thermal model was developed to calculate the temperature field inside early-age concrete. To verify the accuracy of the numerical simulation, the temperature field test during the hardened period of two 1.5 m×1.2 m×4.0 m members were carried out. Meanwhile, FE simulations on the condition of demoulding time at 72 hours, 96 hours, 120 hours and 144 hours after casting were carried out. According to the comparative analysis of numerical simulation results and temperature field test data, the FE simulation of temperature field is in good agreement with the site-measured data, and the maximum cooling rate after demoulding decreases with the extension of the demoulding time, showing that the thermal model established in this paper can accurately predict the hydration temperature field of the large-size concrete member during the hardened period, and the appropriate extension of the demoulding time will lower the temperature cracking risk.