A finite element method for on-line calculation of slab band temperature during hot rolling belongs to the rolling technical field, and comprises the following steps that: (1) the establishment of a finite element model: unit division of the cross section of a rolling piece is carried out to set up a finite element analysis model; unit node numbering is carried out to calculate nodal coordinate; (2) the determination of parameters during calculation: the data needed during calculation includes initial information, rolling parameters, thermal physical property parameters of material, unit division information, control parameters and heat exchange coefficient; (3) the establishment of finite element solving equations set: through combining spatial domain finite element discretization and time domain finite difference, the solving linear equations set of temperature field finite element is set up; (4) pass rolling starting temperature is calculated; (5) on-line application is carried out. The invention has the advantages that: the invention can obtain high temperature calculation precision and the detailed information of slab band temperature distribution during entire hot rolling, thereby providing set parameters and optimized parameters for the rolling process; meanwhile, with strong practicality, the invention reduces calculation time and improves calculation efficiency; moreover, the invention is suitable for online application and optimization.