The invention relates to a double-functional P-N heterojunction and a preparation method and application thereof, belongs to the double fields of gas sensitivity and catalyzing, and relates to electrostatic spinning and hydrothermal techniques, in particular to a preparation method of a gas-sensitive and catalytic double-functional heterogeneous nanometer composite material MoS2-SnO2 (molybdenum disulfide-tin oxide) by using electrostatic spinning and hydrothermal techniques. The preparation method comprises the following steps of (1) dissolving tin salt and a surfactant into ethyl alcohol andN,N-dimethylformamide to prepare a spinning precursor solution; (2) spinning the precursor solution into yarns by the electrostatic spinning technique, and calcining at high temperature, so as to obtain SnO2 nanotubes; (3) mixing and stirring the prepared SnO2, a certain amount of molybdenum salt and a sulfur source, and performing hydrothermal reaction for a period of time at high temperature, so as to obtain the double-functional heterogeneous nanometer composite material MoS2-SnO2; (4) applying the double-functional heterogeneous nanometer composite material MoS2-SnO2 to perform the gas-sensitive property testing and 4-NP catalytic reduction testing. The preparation method has the advantages that the sample preparation is simple, the nanosheet-shaped MoS2 vertically grows at the surface of the nanotube SnO2, and a three-dimensional heterostructure is formed; the excellent properties are realized in the double fields of gas-sensitive and catalytic reduction of 4-NP.