The valley splitting has been realized in the graphene/Ni heterostructure with the splitting value of 14 meV,and the obtained valley injecting efficiency from the heterostructure into graphene was 6.18％[Phys.Rev.B 92 115404 (2015)].In this paper,we report a way to improve the valley splitting and the valley injecting efficiency of the graphene/Ni heterostructure.By intercalating an Au monolayer between the graphene and the Ni,the split can be increased up to 50 meV.However,the valley injecting efficiency is not improved because the splitted valley area of graphene moves away from the Fermi level.Then,we mend the deviation by covering a monolayer of Cu on the graphene.As a result,the valley injecting efficiency of the Cu/graphene/Au/Ni heterostructure reaches 10％,which is more than 60％ improvement compared to the simple graphene/Ni heterostructure.Then we theoretically design a valley-injection device based on the Cu/graphene/Au/Ni heterostructure and demonstrate that the valley injection can be easily switched solely by changing the magnetization direction of Ni,which can be used to generate and control the valley-polarized current.