Graphene is widely used as promising electronic material and devices, owing to its exceptional electronic and optoelectronic properties. Up to now, defect-free graphene has been limited to the method for controllable, reproducible and scalable mass production. A simple, green, and nontoxic approach for large-scale preparation of high quality graphene is produced by exfoliation of graphite sheets collaborated with intercalant (FeCl2) under hydrothermal conditions, the absence of defects or oxides in graphene with a yield up to 10 wt% can be a practical application and industrial process such as optical limiters, transparent conductors, and sensors. This new process could potentially be improved to give a yield of up to 35 wt% of the starting graphite mass with sediment recycling. We show with experiments and theories that exfoliation graphene is the result of a combined action by diminishing the van der Waals interactions between graphite layers and the shear force drove by the Brownian motion of H2O and FeCl2 molecules. Hydrothermal exfoliation has potential applications in the exfoliation of other layered materials (e.g. BN, MoS2) and carbon nantubes, and in the synthesis of intercalation compounds, nanoribbons, and nanoparticles, thus opening new ways of exfoliation engineering.