A frequency regulation method and apparatus is applied to an insulation impedance detection apparatus in a direct current power system, and relates to the field of security monitoring technologies of a direct current electrical system. The method includes: collecting sampling voltages at a sampling point for at least three time points; determining a voltage frequency regulation manner based on the sampling voltages, obtained through sampling, at the at least three time points; and then regulating a voltage frequency of a power supply according to the determined voltage frequency regulation manner. The voltage frequency of the power supply can be regulated based on the at least three sampling voltages obtained through sampling. Therefore, the insulation impedance detection apparatus reduces insulation impedance detection duration while ensuring accuracy of measured insulation impedance.