The present invention discloses a secondary side protection method for a switching power converter, used to turn off a secondary side switch according to a secondary side voltage signal, wherein the secondary side voltage signal has falling edges corresponding to the start instants of secondary side discharge periods, and rising edges corresponding to the end instants of the secondary side discharge periods, the method comprising the steps of: measuring the time interval between two adjacent the rising edges repeatedly to derive discharge end cycle times; and generating a first turn-off signal to turn off the secondary side switch when the relative difference of two successive the discharge end cycle times exceeds a predetermined percentage. The present invention also provides a secondary side protection apparatus according to the method.