The present invention discloses a blank channel searching frequency modulation transmitter, which includes a processor coupled respectively to a frequency modulation (FM) receiver, a comparator, a display, a controller, and a frequency modulation (FM) transmitter; wherein the FM transmitter is connected to a sound input device; the processor determines whether or not the searched channel is used by a radio; if yes, then search for the next channel; if no, then stop searching and use the searched channel to transmit a frequency modulation signal of the sound input device to a radio of the same channel. Therefore, users can listen to music from another sound input device through a blank radio channel without changing the existing radio structure, and the invention achieves the effect of a convenient uninterfered operation.