The disclosed synchro switching control circuit in use for switching power converter with changeable frequencies includes following parts: a first circuit in use for generating a first signal based on an input synchronous signal; being coupled to the first circuit, a second circuit in use for generating a second signal based on frequency of the first signal, and synchronous operation is allowed only when the first signal is operated at a specific frequency range; being connected to the first circuit and the second circuit, an oscillation circuit in use for receiving first signal and second signal, and then generating an oscillation signal; the oscillation signal in use for enabling a switching signal of power converter, therefore the switching signal is synchronous to the input synchronization signal based on enabled second signal, otherwise operation of the switching signal will not be restricted.