The invention provides a digital television single frequency network radio frequency adapter and a broadband network system thereof. The adapter comprises a programmable module, and a broadband radio-frequency signal FM is subjected to down-conversion filtering to acquire a broadband intermediate frequency signal IF1. IF1 is switched in an intermediate frequency gain control module to acquire a broadband intermediate frequency signal IF2 with constant signal power. A/D conversion is performed to acquire a digital signal DATA1, which is switched in the programmable module to form DATA2=DATA1+delta t according to set time delay. The IF2 is subjected to D/A conversion to become a broadband intermediate frequency signal IF3 having accordant frequency domain with the IF2 and delayed time domain, and then the IF3 is subjected to up-conversion filtering to acquire a delayed broadband radio-frequency signal. The broadband network system is provided with the single frequency network radio frequency adapter. A multipath audio/video program source is processed by a front-end information source processing module, a channel processing module and a small signal broadband synthesizer into a small signal broadband radio-frequency signal FM. A signal chain transmits to each node, the single frequency network radio frequency adapter of each node adjusts the signal time delay and each broadband transmitter amplifies and transmits the signal FM, so the stability and covering effect of the system are improved and the cost is lowered.