Based on the statistical analysis and the correlation between high temperature days and synchronous circulation, summer monsoon, and meridional circulation in Guangdong from 1967 to 2007, the long endurance of the high temperature event in July 2007 is studied. Results show that the circulation in July 2007 exhibited the typical features of highfrequency years of high temperature, with the intensified East Asia blocking high, southward extension of subtropical frontal zone, and persistent control of subtropical high over South China, which led to the significant positive anomaly of the number of high temperature days. The urbanization effect on summer maximal temperature increased gradually and speeded up significantly in the last decade. The urbanization effect should be put into consideration in the study of summer high temperatures.