The invention discloses a novel phthalonitrile resin and a preparation method thereof. Compared with a conventional phthalonitrile resin (only 4-nitro phthalonitrile as an end-capping reagent, the novel phthalonitrile resin is introduced with 3-nitro novel phthalonitrile resin to cooperate end capping, and thus the asymmetry of a resin structure is increased and the turbidity of a resin component is increased (see a formula 1). Compared with the conventional phthalonitrile resin, the novel phthalonitrile resin disclosed by the invention has the characteristics of low melting temperature, good solubility, wide processing window, low curing temperature and the like; a prepared resin molded part and a resin-based composite material are low in porosity, excellent heat-resistant quality, and high in mechanical property, and can be applied to the fields of aerospace, a space technology, machine manufacturing, and the like as a light-weight and high-temperature resistant part. The formula is described in the specification.