The power system of Beijing is a complex giant system. The risk of peak power load supply under the extreme high temperature weather was prominent, and there was few research about the scientific and reasonable method to determine the assessment indexes on the extreme weather risk. The risk-causing mechanism of power system under the influence of extreme temperature was analyzed. Based on the analysis of energy flow in life cycle, the network structure model of Beijing power system was constructed from the aspects of power production and transformation, power transmission and distribution, and power terminal consumption. The network structure weight of each link factor was quantified by the Gephi software using graph theory analysis method, and the extreme weather risk assessment indexes of power system were determined. The analysis showed local power, external power, urban transmission and distribution network and tertiary industry consumption were at the higher level in the importance of system structure. Inner Mongolia was the most influential source of external power for Beijing, and natural gas was the most influential basic energy for local power supply. The Anding 500 kV hubs have the greatest degree of correlation among the key stations affecting the power transmission and distribution of Beijing.