Abstract: The cyber physical power system （CPPS） brings some potential risks for the smart grid， which is caused by the complex mechanism in the coupling process between the primary system and the secondary system. This paper proposes a CPPS security situation assessment model that considers threat propagation. First，  the CPPS is abstracted into a network. Assets in the power system are defined as network nodes， and the connections those exist between assets are defined as the edges of the network. Then， the threat propagation is defined between assets as a threat propagation tree， and the importance of each asset in the CPPS is quantitatively evaluated. Finally， a decision-making membership function is applied to the accuracy and timeliness of the scene， and the improved threat propagation tree is used to evaluate the situation on the basis of the filtered information. Through the example analysis on the IEEE 30-node system， the simulation results verify the feasibility and effectiveness of the proposed model.

Key words: cyber physics power system （CPPS）, security situation assessment, threat propagation, complex network