The measurements and simulations using finite element software are carried out on the cast temperature field as well as the related thermal stress field in zero blocks of segmental high-strength concrete box girder. The thermodynamic parameters, to some extent dominating the effectiveness of the simulation, are determined carefully in terms of the statistical data, the empirical formulas as well as the measured data in an actual project, which leads to reliable simulation results by means of the finite element software. The comparison between the calculated and measured values of temperature field shows that the maximum error among all measuring points is only 1.71%. Meanwhile, the predicted directions of principal tensile stress coincide with the actual directions of the observed cracks well. Based on the above work, the common features of the cast temperature field caused by heat of hydration are obtained for this kind of structures. The relationships of the cast temperature field, the thermal stress, and the early-age cracks are discussed quantitatively in order to provide reasonable suggestions for temperature control and crack prevention in similar projects.