The invention provides an LLC series resonance-based low-voltage stress single stage AC-DC convertor, which comprises an input rectification filter circuit consisting of an input rectification circuit (E) and a rectifier bridge (Q), a buck-boost circuit consisting of an inductor (L), a first switching tube (S1), a third diode (D) and a first capacitor (C), an output rectification filter circuit consisting a first diode (DO1), a second diode (DO2) and a third capacitor (CO), and an LLC series resonant inverter circuit consisting of a first switching tube (S1), a second switching tube (S2), a first capacitor (C), a second capacitor (Cr), a transformer (T), a leakage inductor (Lr) and a magnetic inductor (Lm). The convertor realizes input power factor correction and the functions of voltage boost and voltage buck, has wide output voltage regulation range, uses less switching tubes, is high in efficiency and low in cost, and can be used as an LCD power supply.