The invention discloses a liquid-phase synthesis method of non-physically adsorbed Au/TiO2 composite nanoparticles and heterojunctions. The liquid-phase synthesis method comprises the following steps: carrying out surface disordered amorphous reconfiguration treatment on TiO2 nanoparticles dispersed in a formaldehyde solution by means of optical irradiation, electrostatically adsorbing [Au(OH)4]-radical groups on the surfaces of non-crystallized TiO2 nanoparticles; realizing in situ Au reduction under liquid-phase hydrothermal conditions to obtain non-crystallized transition Au-TiO2 composite particles; and synthesizing the Au/TiO2 composite nanoparticles by high-pressure hydrothermal secondary crystallization. According to the liquid-phase synthesis method provided by the invention, the effective coupling between interfaces of Au nanoparticles and TiO2 nanoparticles is realized, the composite Au/TiO2 nanoparticles are prepared, and the size of Au particles can be conveniently controlled according to the needs of practical application.