The extremely high temperature(≥40℃) that occurred in Zhengzhou duri ng 22—23, June 2005 is analyzed by utilizing the 1°×1°grided data of NCEP/NC A R. The results show that the Hetao high is an important synoptic system that cau sed the extreme hot weather in Zhengzhou and even the western part of the Huang- Huai region. The generation of the Hetao high is concerned with the warm advecti on at various levels. The appearance of the extremely high temperature is also r elated to the upper level subtropical jet stream. The strong descending air flow in the southeastern part of the Hetao high is caused by both thermodynamic and dynamic factors. That is, when the southeastern part of Hetao high lies in the l eft side of entrance region of the upper level subtropical jet stream, dynamic c onvergence makes the descending movement of air flow in this region more powerful. The consequential clear radiation heating and adiabatic warming because of ai r sinking benefit the occurrence of extremely high temperature. In addition, the foehn effect generated by topography can be of a role of intensifying the extre me high temperature.