To discover the reasons of the strong vibration and unease of a light-bus, the methods of analysis vibration transfer function and road test was used，and found that it was caused by the softer stiffness of engine suspension cushion, which led to the lowest proper frequency of engine suspension system below the allowable value. Two decreasing vibration projects were put forward, which only improved the stiffness of the engine suspension cushion. For project one, the lowest proper frequency of the light-bus engine suspension system was 3.75 Hz which was within permission range. Furthermore, the maximal amplitude value of vibration transfer function descended obviously and the weighting acceleration RMS value was smaller than project two, so it could achieve better effect of isolating vibration.