The invention relates to a Pd-doped rGO / ZnO-SnO2 heterojunction quaternary composite material as well as a preparation method and application thereof, and belongs to the technical field of gas sensors. The composite material is secondary particles formed by agglomeration of primary particles, the primary particles take rGO of a two-dimensional net structure as a matrix, the surface of the matrix is coated with sheet nanometer materials ZnO and SnO2, ZnO and SnO2 are compounded to form n-n type heterojunctions, ZnO, SnO2 and rGO respectively form p-n type heterojunctions, and Pd nanoparticles are doped in ZnO, SnO2 and rGO. The method comprises the following steps: firstly, mixing a flaky ZnO nano material and stannous chloride in water, sequentially adding DMF, sodium hydroxide and palladium chloride to obtain a mixed solution, then carrying out hydrothermal reaction on the mixed solution and a graphene oxide dissociation solution, and finally calcining. The composite material has the characteristics of high selectivity, quick response and low-concentration detection when being used in the hydrogen sensor.