False data injection (FDI) attacks pose a great threat to the safe operation of power grid. By attacking nodes with weak defences

high transmission risks and high returns

attackers can cause more damage to the power grid with limited resources. Therefore

it is of great significance to evaluate these critical nodes for active defence of power grid. This paper presents an evaluation index and defence method of critical information node. Firstly

by establishing an FDI attack model

information system model and attack propagation model

quantitative analysis is carried out on basic indicators

such as attack return

attack success probability

transmission risk

transmission intensity and correlation

between attack return and transmission risk of information nodes under FDI attack scene. According to the attack detected and no attack detected scenes

the basic evaluation indexes were selected

respectively

to establish a comprehensive evaluation index. Finally

based on the comprehensive evaluation index

two defence methods are proposed to improve the power grid's ability to resist FDI attacks

respectively

applicable to detected attacks and undetected attacks. The effectiveness of the proposed evaluation index and defence method is verified by the simulation results of IEEE57 nodes system.