A heat dissipation device in a computer enclosure includes a heat spreader (20) mounted on a CPU (12), a first heat sink (30), a cooling fan (40) coupled to the first heat sink, a second heat sink (50), a heat pipe (80) mounted on the heat spreader and thermally connected the first heat sink and the second heat sink, a system fan (60) attached to the second heat sink, and a fan duct (70) interconnected between the cooling fan and the second heat sink. The system fan is positioned adjacent to louvers of the computer enclosure. An airflow generated by the cooling fan and the system fan flows through the first heat sink, then the fan duct, the second heat sink, and finally the louvers to leave the computer enclosure.