Abstract: There has been an increasing focus across society on the situation of electricity demand and supply as well as the security of electric power. The unexpected frequency, intensity and duration of extreme weather introduce significant uncertainty into the short-term electric power supply security. In this paper, based on practical experiences of national electric power supply, systematic reviews are conducted for the main factors affecting electric power demand and supply during the summer and winter peak. These factors include the extreme weather, the structure of the power sources, the supply of primary energy, and unplanned outages. In light of the above factors, further measures are proposed aiming to construct a diverse and comprehensive supply security system.