A fan noise-lowering structure includes a fan frame main body and a connecting pipe. The fan frame main body has a bottom section and a peripheral wall section; the peripheral wall section is externally located around and forwardly extended normal to the bottom section and internally defines an air-stream passage. Further, the peripheral wall section is formed with a first pipe and a second pipe, which are communicable with the air-stream passage defined in the peripheral wall section. The connecting pipe has two ends respectively connected to the first pipe and the second pipe. With the connecting pipe, air at an air outlet of the air-stream passage having higher pressure is guided to generate swirls, which moves toward an air inlet of the air-stream passage to thereby effectively lower the noise produced by the fan in operating.