Abstract: The cable trench is used to lay the low-voltage power cable,control cable,communication cable and optical cable of the power system in substation,which is an important channel for power transmission and information transmission.Once the cable in the trench catches fire and spreads,the power and information of the whole substation will be interrupted,resulting in serious power grid accidents. The research on fire spread trend is the basis of realizing cable fire early warning,automatic fire extinguishing and improving the fire protection ability of the line. The simulation model of substation cable trench fire spread based on finite element method was established.The influence of different layered laying methods on the fire spread trend of cable trench was studied.It was found that the fire spread in cable trench is mainly longitudinal,and therefore reducing the number of cable layers can effectively delay the development of fire and reduce the loss of cable fire.The layered cable laying method has little effect on the temperature field of cable trench after fire.In the process of cable trench fire,there is a significant stratification phenomenon in the temperature field and toxic gas concentration distribution.