An exemplary CPU frequency regulating circuit includes a detecting circuit, a comparing circuit, and an adjusting circuit. The detecting circuit is coupled to a power circuit of a CPU for receiving and amplifying a load voltage. The comparing circuit is coupled to the detecting circuit for comparing the amplified load voltage with a default voltage. The adjusting circuit is coupled between the comparing circuit and the CPU for selecting a CPU frequency according to a result of the comparison. The CPU frequency regulating circuit detects the load voltage of the power circuit of the CPU for selecting an appropriate frequency to the CPU according to a working condition.