A multi-mode hybrid control DC-DC converting circuit has a switching power converter and a microcontroller. The switching power converter has a transformer and a switching switch. The switching switch is connected to a primary-side winding of the transformer in series. The microcontroller is connected to the switching power converter and a control terminal of the switching switch. The microcontroller sets multiple thresholds according to an input voltage of the switching power converter, and determines whether a feedback voltage of the switching power converter is higher or lower than each one of the thresholds to perform a variable-frequency mode, a constant-frequency mode, or a pulse-skipping mode. The microcontroller outputs a driving signal to the switching switch and correspondingly adjusts a frequency of the driving signal according to the variable-frequency mode, the constant-frequency mode, or the pulse-skipping mode which is performed.