This application discloses a signal generating method, apparatus, and system. One example method includes: performing cyclic electro-optic modulation on a first signal to generate a first optical frequency comb signal, where the first signal is a signal output by a laser source, the first optical frequency comb signal includes a target spectral component, and a frequency of the target spectral component is equal to a sum of or a difference between a frequency of the first signal and a frequency of a target signal; performing first filtering processing on the first optical frequency comb signal to generate the target spectral component; and generating the target signal based on a heterodyne beat frequency of the first signal and the target spectral component.