The cracking control standard of water delivery structure is quite strict especially for middle-route of south-to-north water transfer project with long distance water transfer, large discharge, the crack prevention standard is extraordinary strict and must be reached. Early crack during construction period will affect safe operation of aqueduct, and diurnal variation of air temperature has significant effect on temperature field of thin-walled structure. Construction process simulation and temperature filed calculation during construction period about Caohe river landing rectangle aqueduct of Beijing-Shijiazhuang emergency water supply engineering of middle-route of south-to-north water transfer project are carried out by FEM , and compared with the monitoring temperature. The comparison result shows that temperature field during construction can be accurately simulated by calculation, which is helpful for guiding construction and choosing construction scheme, and worthy to popularize to other similar projects. From the calculation and monitoring, the maximum temperature difference is less than the standard, so there will be no serous cracks during construction in Caohe river aqueduct.