The invention provides an isolated high-gain quasi-Z source DC-DC converter, including mainly the input DC voltage source, by the first inductor, first capacitance, first diode, a quasi-Z source network composed of a second inductor and a second capacitor, by the second diode, a quasi-switching boost unit composed of a third diode, a third capacitor, a third MOS transistor and a fourth MOS transistor, a first MOS transistor, a second MOS transistor, a high-frequency transformer T with a conversion ratio of 1: n, a voltage doubling rectifier composed of a fourth capacitor, a fifth capacitor, afourth diode and a fifth diode, and a load resistance R (i) L ( / i). The whole circuit is simple, The input current of the power supply is continuous, which combines the single step-up and step-down voltage characteristics of the quasi-Z source impedance network and the quasi-switching boost network respectively, so that the output voltage gain is higher, and the electrical isolation between the output and input of the converter is realized by a high-frequency transformer, and the circuit does not have the start-up impulse current and the impulse current of the switching transistor at the turn-on time.