The high AC/DC hybrid system is the development direction of power grid in the future

and the large-scale power transmission makes the system’s failure process and influence more complex and serious

however

the analyses of traditional grid security usually focus on the form and process of failure. Therefore

in order to better quantitatively analyze the extent of the system abnormality

we put forward a safety analysis method of ultra high AC/DC system based on the risk assessment theory. According to the characteristics of UHV AC/DC system

the safety analysis modeling is carried out based on risk assessment theory. The new model fully considers the interaction of ultra high AC/DC hybrid system

which makes the analysis model more suitable for the UHV AC/DC system. The power grid security analysis conbines the system security and influence degree in the new model. The actual application results of the analysis model also show that the method are clear

can be effectively combined with the widely used PSASP（Power System Analysis Software Package） or BPA（Bonneville Power Administration） system simulation software

and has the advantages of easy realization

extensibility

and applicability.