The invention relates to a reverse-current-prevention protection circuit of an LDO (low dropout regulator). On the basis of an existing LDO, a reverse-current-prevention circuit and a reverse-current-prevention NMOS (N-metal-oxide-semiconductor) transistor are arranged, the reverse-current-prevention circuit is connected among an input terminal VIN, an output terminal VOUT and a substrate of a power PMOS (P-channel metal oxide semiconductor) transistor, a drain and a source of the reverse-current-prevention NMOS transistor are connected between a feedback divider resistor and a ground terminal, and VIN potential and VOUT potential are compared by the reverse-current-prevention circuit, so that a substrate of the power PMOS transistor is switched to be selectively connected with the highestpotential between VIN and VOUT, the parasitic diode effect fixed between the substrate Bo and the drain of the power PMOS transistor MP is broken, an output logic signal of the reverse-current-prevention circuit is connected with a grid of the NMOS transistor, a reverse current produced by the parasitic positive bias diode effect of the power PMOS transistor can be avoided between output VOUT andinput VIN, and loss and damage of the power PMOS transistor are effectively prevented.