The invention relates to a method for preparing a graphene modified copper-based electrical contact material through an in-situ growing process. The method comprises the following steps that firstly,graphene coated pure copper powder is prepared through an in-situ chemical vapor deposition process, then the graphene coated pure copper powder, copper alloy powder and zinc stannate powder are uniformly mixed by adopting a mechanical ball milling process, so that the composite powder is obtained; then a cold isostatic pressing forming process and a pressureless sintering process are adopted to obtain an electric contact sintered blank, finally, a hot extrusion process and a cold rolling process are performed to obtain the graphene modified copper-based electrical contact material with good structure. According to the method, a graphene reinforcing body is introduced into the copper-based electrical contact material through the in-situ chemical vapor deposition process, so that the cost of the graphene raw material is greatly saved, the technological effect that the graphene is uniformly dispersed in a copper base body is achieved, the mechanical strength and the electric arc ablationresistance of the contact material are remarkably enhanced while the electric conduction performance and the heat conduction performance of the contact material are not reduced.