The dynamic behavior of roller system of a "1+4" hot strip rolling tandem mill were analyzed. The stochastic vertical vibration and the optimum mathematical model were established based on the reliability after the system simplified to some extent. Stochastic optimum has been done to the system according to the optimum mathematical model of the roller system. Its best natural frequency and damping coefficient are obtained by computer simulation under the situation of minimum response of the rollers stationary acceleration when chatter occurs. The results indicate that by optimizing the natural frequency and damping coefficient of the system can greatly improve the dynamic behavior of rollers system and equality of the strip, and are useful to the new design of the rolling mill and the setting up of the rolling parameters.