An extended fin array has a main heat-dissipation module and an extended heat-dissipation module. The main heat-dissipation module and the extended heat-dissipation module are stacked to increase the effective convective area to increase the heat-dissipation effect. The extended heat-dissipation module is in the main heat-dissipation module when the heat amount generated by an electronic device is normal. The extended heat-dissipation module extends out from the main heat-dissipation module to increase the heat convection area when the heat amount generated by the electronic device is large.