A wing-spanning thermal-dissipating device has a plurality of thermal-dissipating sheets. Each of the thermal-dissipating sheets includes a connecting portion, at least one thermal-dissipating fin and a plurality of sub-thermal-dissipating fins. The connecting portions of the thermal-dissipating sheets connect with each other. The thermal-dissipating fin is extended outwardly and spread out from the connecting portion. The sub-thermal-dissipating fins are extended from at least one side of the thermal-dissipating fin.