A frequency dividing system, which comprises a control circuit, a first multiple input sharing input level triggering device, a first input level triggering group and a second input level triggering group. The first multiple input sharing input level triggering device receives a first frequency dividing signal to generate a feedback signal according to a level of a first clock signal, or receives a second frequency dividing signal to generate the feedback signal according to a level of a second clock signal. The first/second input level triggering group generates the first/second frequency dividing signal to the first multiple input sharing input level triggering device according to the feedback signal if active; and outputs a fixed voltage to the first multiple input sharing input level triggering device if non-active.