A heat dissipation device of a vehicle lamp and an interposing element thereof are provided. The heat dissipation device is installed in a lamp room which is divided by the interposing element into a front partition and a rear partition. A heat sink is installed in the interposing elements. An air feeding fan is disposed in an air feeding channel of the interposing element, for drawing air in the front partition to the rear partition through the air feeding channel. Further, a back flow fan is disposed in the rear partition, for drawing air in the rear partition to the front partition through a back flow channel. Whereby, the air in the front partition is cooled down through an external air flow passing through the lamp cover. Then, the heat sink dissipates heat of the air flow with the relatively low temperature in the front partition to the rear partition.