The invention relates to an environment treatment technology and particularly relates to a porous Cu2-xSe photocatalyst and a preparation method. The preparation method comprises the step of preparinga Cu2-xSe sheet by adopting a solvothermal method. The porous Cu2-xSe photocatalyst and the preparation method have the beneficial effects that since ethanediamine is used as a solvent, the dissolution of Se can be promoted, and the benefit for formation of the porous shape can be achieved, so that the specific surface area is enlarged; under excitation of visible light, the porous Cu2-xSe sheetcan degrade organic matters completely in 30 minutes, and the photocatalytic property is stable after 4 times of circulation.