The invention relates to a method for judging the GaN doping type of an HVPE epitaxial growth sapphire substrate through ultraviolet-induced hydrophilia. The method includes the specific steps that a to-be-tested GaN sample is irradiated by an ultraviolet lamp, after the sample is irradiated by the ultraviolet lamp, if the contact angle of the to-be-tested GaN sample is reduced by at least 10 degrees than that generated before the GaN sample is irradiated by the ultraviolet lamp, the to-be-tested GaN sample is N type GaN, or else the to-be-tested sample is P type GaN. According to the judgment method, consumed time is short, the test result can be rapidly obtained, and compared with a prior judgment method, complex operation of multi-data-point acquisition and following data processing is omitted. According to the method for judging the GaN doping type, the surface contact angle of the N type GaN sample irradiated by ultraviolet can be restored to an original state after being put in dark for about three days, no damage such as electrode preparation to the surface of the tested sample is generated, and the sample can be applied to other experiments after testing is over.