A heat dissipation device includes a heat spreader (20), a heat pipe (30), a heat sink (40) and a cooling fan (50) for generating forced airflow to the heat sink. The heat pipe has an evaporating section (301) being thermally attached to the heat spreader and a condensing section (302). The heat sink has a fin assembly defining a plurality of channels (405) for the airflow flowing therethrough. Each of the channels has at least one portion with a width being gradually decreased along the flowing direction of the airflow. The channels (405) each are defined between two adjacent fins (401, 402), wherein at least one of the two adjacent fins is arc-shaped.