The main causes of the high temperature weather occurred in Zhangjiakou in late July 2010 are analyzed by using the data from weather maps, NCEP reanalysis data and ground observations, based on the heat flow equation. The results show: (1) High temperature appeared in the background of the steady control of the mainland high. (2) Under the control of the mainland high, the non adiabatic condition was the key factor leading to high temperature, while the thermal advection had less effect. (3) Higher surface temperature and the longer duration may also make some contributions to the new record breaking high temperature on July 29 2010. (4) The maximum temperatures were compared with the corresponding 850 hPa temperatures at 14:00 of the hot days, and a difference of 9 ℃ between them can be used as a suitable reference in maximum temperature forecasting.