We exploit graphene square-ring to realize coherent perfect absorption (CPA) in the terahertz (THz) regime. The simulated results show a 90% absorption coefficient over a wide range of angles of incidence for both TE and TM radiations. The coherent absorptivity is tunable from nearly 0% to 100% by adjusting the relative phase of two low power counter-propagating coherent beams. The central frequency of the absorption simply can be tuned by varying the chemical potential of graphene and by changing the geometric parameters of metasurface. Thus, the proposed absorber is very promising for various optical applications as modulators, detectors and electromagnetic switches. This article offers a novel path for perfect absorption in THz gap, it should be noted that the thickness of proposed absorber is only about λ/4.