In order to solve the problem of the bowing phenomenon in the tentering process of film, the stretching and thermosetting conditions were examined with a poly (ethylene terephthalate) film. The simulated and experimental results confirmed that decreasing or preventing the transmission to the next thermosetting zone of the longitudinal force generated by the transverse stretching, and then restretching the film in the thermosetting zone, effectively reduces the bowing distortion. The following effects were observed : (1) Once the film is cooled after stretching it in a tenter, the different patterns of its deformation behavior can be obtained. The bowing distortion changes remarkably with the temperature of film and the length of the cooling zone. (2) When the temperature of the cooling zone is not higher than the glass transition point, the effect of the cooling zone in reducing the bowing distortion is at its maximum. The longer the cooling zone is, the less the bowing distortion becomes. However, it becomes almost constant when the length of the cooling zone is at least twice the width of the film. (3) When the cooling zone is set up between the stretching and thermosetting zones, the bowing distortion is almost independent of the thermosetting temperature. (4) Relaxation and restretching in the transverse direction in the thermosetting zone influence the bowing distortion : greater relaxation results in greater bowing distortion and greater restretching results in the less bowing distortion.