A signal transmission system includes a first clock signal generator and a second clock signal generator. The first clock signal generator is configured for generating a first clock signal according to clock information derived from a transmitted signal, wherein the transmitted signal is changed in response to a frequency change of a second clock signal, and the first clock signal generator enters a frequency-unlocked state if the second clock signal has a frequency transition from a first frequency to a second frequency during a first time period. The second clock signal generator is configured for generating the second clock signal having the frequency transition from the first frequency to the second frequency during a second time period longer than the first time period such that the first clock signal generator stays in a frequency-locked state during the second time period.