Web tension control system recently have been applied to OLED(Organic Light-Emitting Diode), RFID of flexible material, e-Paper and PLED(Polymeric LED) and various web control algorithms have being developed for higher productivity and product quality These system need an accuracy model to design and implement controller. In this paper, the web tension control system with dancer roll is mathematically modeled. Mathematical model consists of 8 subsystems and each subsystems can be described as impedance structure which connected by velocity and tension. Mathematical model is different from the estimated model at high frequency range because of structure dynamics which is ignored on mathematical model. The estimated model is derived using ARMAX model. The controller is designed using the estimated model. The step response of the estimated model are compared with that of physical model for a validation of estimated model. The experimental results show a good match between them.