Advanced photocatalytic systems are actively pursued to address a large number of pressing issues facing chemical engineering in applications. In the photocatalytic process, high-performance catalysts well beyond the current capacity and cost of platinum-carbon composites are required. In this work, Pt/g-C3N4 composite photocatalysts were synthesized using a low-temperature inductively coupled plasma technique to substantially improve the photocatalytic performance for hydrogen production. After the plasma reduction of H2PtCl6, ultrafine Pt nanoparticles were uniformly deposited on g-C3N4. By changing the plasma discharge power, the size of Pt nanoparticles, the composition and electronic structure of Pt and the interaction between Pt and g-C3N4 can be effectively controlled. Moreover, Ar plasma modified the surface structure of g-C3N4 to form new active oxygen-containing groups. The Ar-plasma-treated Pt/g-C3N4 composites showed excellent activity for hydrogen evolution under visible light. When Pt/g-C3N4 composite was plasma-treated at 150 W for 40 min, the achieved hydrogen production rate was 1150.8 μmol/h, which is about 63.2 and 4.6 times higher compared to the pristine g-C3N4 and Pt/g-C3N4 composite prepared by the photodeposition method, respectively. Our results indicate that the low-temperature inductively coupled plasma treatment is an effective and promising tool to fabricate high-performance catalytic materials.