Graphitic carbon nitride (g-C3N4) is a promising metal-free photocatalyst for solar photo catalytic hydrogen gas (H-2) generation from water. In particularly, high-crystalline g-C3N4 (GCN-HC) material with fewer structural defects possesses the fast photoexcited electron-hole pair's separation efficiency as comparison with bulk g-C3N4 (GCN-B) powders, leading to the drastic improvement of photocatalytic activity. However, the fabrication of such GCN-HC photocatalyst by a simple and economical synthesis approach still remains a challenge. Herein, we firstly develop a one-step rapid polymerization strategy for synthesizing the GCN-HC, that is direct calcination of melamine at 550 degrees C not only without the early heating process, but also without the assistance of any additive or salt intercalation. As a result, the GCN-HC exhibits an obviously boosting visible-light-induced photocatalytic H-2-generation performance, which is over 2.06-folds much greater than that of GCN-B. Our work provides an available one-step synthetic strategy for the large-scale preparation of high performance GCN-HC towards sustainable solar-to-chemical energy conversion. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.