A heat dissipating device includes thermal conductive pipes and a plurality of thermal fin modules. Each thermal fin module made by pressing and stacking is mounted on the thermal conductive pipes. A retainer is located between each two thermal fin modules to compress the thermal fin module, so that a distance between two fins of the thermal fin module is reduced. Finally, a fixing plate is set above the last thermal fin module on the thermal conductive pipes to fix the thermal fin modules securely engaged with the thermal conductive pipes. Therefore, the assembled heat dissipating module could not be loosed and deformed during delivery and the engaging contact between the fins and the thermal conductive pipes are enhanced, so to increase the heat dissipating effect of the heat dissipating module.