A dual-function transmitting system is provided. The dual-function transmitting system includes a receiving module, N combining modules, N transmitting modules, and M signal providers. After receiving a CATV signal and an Ethernet signal, the receiving module transfers the Ethernet signal into a RF signal. Each of the N combining modules combines the CATV signal and the RF signal transferred from the receiving module to generate a combined signal, respectively. Each of the N transmitting modules is coupled to one corresponding combining module and transmits the combined signal received from the corresponding combining module. Each of the M signal providers is coupled to one corresponding transmitting module, receives the combined signal transmitted from the corresponding transmitting module, and provides the CATV signal and the RF signal comprised in the combined signal, respectively.