The invention discloses a photovoltaic system-used cascaded multi-bootstrap DC-DC converter. The photovoltaic system-used cascaded multi-bootstrap DC-DC converter comprises an input power supply Vin;the positive electrode of the input power supply Vin is connected with one end of an inductor L1; the other end of the inductor L1 is respectively connected with the anode of a fly-wheel diode D1 andthe anode of a fly-wheel diode D2; the cathode of the fly-wheel diode D1 is respectively connected with one end of a primary winding L2 of a coupling inductor, one end of a capacitor C1 and one end ofa clamping capacitor Cb; the other end of the primary winding L2 of the coupling inductor is respectively connected with the anode of a fly-wheel diode D4, one end of a capacitor C3, the cathode of the fly-wheel diode D2 and the drain of a switch transistor S; the other end of the capacitor Cb is respectively connected with the cathode of a clamping diode Db and the anode of a fly-wheel diode D3;the other end of the capacitor C3 is respectively connected with the anode of the clamping diode Db and one end of a secondary winding L3 of the coupling inductor; and the other end of the secondarywinding L3 of the coupling inductor is respectively connected with the cathode of the fly-wheel diode D4 and one end of a capacitor C2.