The invention discloses a switching power supply, a primary control chip and a loop compensation device thereof. The loop compensation device comprises: an error amplifier; a switching logic gate, wherein the input end of the switching logic gate is connected with the output end of the error amplifier; a loop compensation capacitor, wherein one end of the loop compensation capacitor is connected with the output end of the switching logic gate, and the other end of the loop compensation capacitor is grounded; and a delay generation circuit, wherein the output end of the delay generation circuit is connected with the control end of the switching logic gate, and the delay generation circuit is used for outputting a valid switching control signal within a preset time after a power switch of the switching power supply is turned off to control the switching logic gate in a turn-on state, so that the loop compensation capacitor is charged/discharged by means of an error amplification signal outputted from the error amplifier. With the loop compensation device, the problem that the output ripple from the switching power supply is too large can be solved, and the loop stability is ensured.