Abstract: The preparation of prepreg tape required spreading the fiber tow to facilitate resin impregnation. Traction tension is the driving force for fiber bundle spreading, but current fiber tow-spreading models rarely involve the effect of traction tension. Aiming at the spreading process of fiber tow on mechanical rollers, combining force analysis, the input work, and the friction work along the axial and lateral directions can be computed. Then the fiber tow spreading model can be established by energy conservation law. Utilizing the pre-dispersion device with mechanical rollers which was built by laboratory, contrastively validate and analyze the spreading model. The results indicate that traction tension is an important reason for fiber tow spreading. And the numbers, radius, smoothness of mechanical rollers, and the wrap angle between the fiber tow and the roller all affect the fiber tow spreading. Compared to the Wilson spreading model, the energy-balance spreading model can better predict the spreading width of fiber tow, and it can be used to guide the pre-dispersion process of fiber tow.