A frequency adjustment method is provided for adjusting a frequency of a reference oscillating signal from an initial oscillation frequency to an adjusted oscillation frequency. The frequency adjustment method includes steps of: dividing a frequency scan section into M scan frequencies; down-converting a signal according to the M scan frequencies to obtain M down-converted signals; performing a correlation calculation operation on the M down-converted signals, respectively, to obtain M correlation results; grouping the M scan frequencies into N frequency groups each containing P selected frequencies, with the P selected frequencies corresponding to P consecutive scan frequencies; performing a group calculation on the N frequency groups, respectively, to obtain N group calculation results; and selecting a target frequency group from the N frequency groups according to the N group calculations results, and obtaining the adjusted oscillation frequency from the target frequency group.