To study the heat rejection law of office building air-conditioning refrigeration system with a large heat rejection per unit building area, one office building in Shenzhen and three office buildings in Beijing in the center of the city were selected as the main research objects, and the heat rejection from air-conditioning refrigeration system through cooling tower was discussed in two forms:sensible heat and latent heat in the field measurement method. This field study results show that the total heat rejection from building air-conditioning refrigeration system per unit building area has a daily average value in the range of 85~106 W/m2, where the sensible and latent heat share the proportion of 1%~5% and 95%~98.85% respectively. It indicates that office building air-conditioning refrigeration system releasing the condensing heat into the outdoor environment through cooling tower is mainly in the form of latent heat, which has a significant effect on the building surrounding humidity environment. Finally, higher temperature and humid outdoor climatic conditions are not conducive to the heat and moisture rejection from the building air-conditioning refrigeration system.