At present ride comfort is one of the important performances of the vehicle. And the towing attachment plays an important role in the longitudinal ride comfort of a tractor trailer combination. This paper studies the influences of the factors of the towing attachment and the speed of the combination on the longitudinal ride comfort of the tractor trailer combination by experiments. The results indicate that the longitudinal ride comfort of the tractor trailer combination will be improved if to a reasonable extent the stiffness of the towing attachment is reduced, or (and) the damping coefficient of the towing attachment is increased, or (and) the speed is reduced. Among the three parameters analyzed, the stiffness of the towing attachment is the most important one for the longitudinal ride comfort of the tractor combination, the speed is the second one, the damping coefficient of the towing attachment is the third one.