Based on electro-thermal coordination（ETC） theory， combining with electro-thermal coupling discipline of transmission element and traditional methods， a dynamic optimal power flow model， which considers the thermal limit， i.e.， the maximum permissible temperature of transmission element， is established. It can take advantages of the thermal inertia characteristic of transmission element in operation dispatch to exploit the full transmission capability of transmission elements. Based on this idea， the model is converted into the algebraic form by adopting numerical integrating method， and then it is solved by inter-point method. In addition， according to the characteristics of this model， the discipline of electro-thermal coupling and the corrected equations' characteristics in the iterative process of inter-point method are investigated. To reduce the solving complexity and improve the solution efficiency， the constrains reducing technology and decoupled treatment on model and algorithm are proposed respectively. Finally， a simulation is carried out to demonstrate the validity of the proposed model and algorithm.