The invention relates to a preparation method of a polymer film porous three-dimensional organic gas sensor. The preparation method includes: a glass substrate (1) and a Mo/Al/Mo bottom grid are used,an intermittent growth method is used to perform polyvinyl alcohol (PVA) spin coating and a continuous growth method is used to perform polystyrene (PS) spin coating to form a compound insulating layer (3) so as to form a flat insulating layer surface; a nucleation growth method is used to grow a p-sexiphenyl (p-6P) induction layer (4), a method combining fast evaporation and slow evaporation isused to evaporate vanadyl phthalocyanine (VOPc) to form a porous gas sensitive layer (5), and an evaporation gold material is used as the interdigital electrode of bottom contact. The porous gas sensitive layer provides three-dimensional direct contact channels for the interaction between analyte and charge carriers in conduction channels, and the organic gas sensor which is high in sensitivity and fast in response can be obtained.