Abstract: There was a huge thermal stress of concrete in box girder during its hardening for the large concrete volume and the hydration heat of cement. The temperature field and the stress field of box girder were analyzed by the finite element method for transient thermal stress, in which its temperature field and stress field were analyzed during different periods after concrete pouring and its disadvantageous bearing positions during cement hydration were summarized. Meanwhile in order to degrade the hydration heat, the hydration heat of concrete containing different quantities of cement was analyzed. Results showed that the thermal stress of box girder was reduced by low-heat cement, which indicated the cracking risk of concrete was reduced.