Three-dimensional (3D) architectures of graphene are of interest in application in electric, catalysis devices, and sensors. However, the fabrication of macroscopic 3D architectures of all graphene under a mild condition still remained a challenge. Here, a simple method for preparation of 3D architectures of graphene is developed via an in situ self-assembly of graphene prepared by a mild chemical reduction at 95°C under atmosphere press without stirring. No chemical or physical cross-linkers and high press are required. The reducing agents include NaHSO3, Na2S, Vitamin C, HI, and hydroquinone. Both graphene hydrogels and aerogels can be prepared by the method, and the shapes of the 3D architectures can be controlled by changing the types of the reactors. The 3D architectures of graphene are in low density, high mechanical property, thermal stability, high electrical conductivity, and high specific capacitance, which make them as candidates for potential application in supercapacitors, hydrogen storage and supports for catalysts.