A method for measuring the ultraviolet spectrum characteristic of Au photocathode has been put forward. Making use of the high gain characteristic of microchannel plate (MCP) and ultraviolet light, the frequency response of Au cathode has been studied by measuring the output current of Au coated MCP detector directly. Through measuring the response current of Au coated MCP detector between 200—340 nm, the selective photoemission of Au has been found, which had been found only for alkali metals. And the selective peak is at 5.72 eV, which can be explained by quantum mechanics theory.