Dual-coiler is one of the most advanced coiling equipment designed for collecting strips in the rolling mill production line for the purpose of storing/transportation. The quality of the steel strip is largely affected by the tension force. This paper devotes to investigate the fluctuating tension force on the steel strip during the coiling process. The dynamics model of driveline is built for simulate the transmission error which is the main cause of the fluctuating tension force. In the proposed model, the time-varying meshing stiffness and damping, and the stiffness of strip are considered. A set of data are measured from the production line for evaluating the presented model. It’s believed that the proposed model can be used for improving the mechanical design of the machine.