The invention provides a method and a device for processing to adjust image luminance. The method mainly comprises: decomposing image signal into background signal and scenery signal; processing a normalized adjustment treatment for the luminance of the background signal and normalizing the scenery signal and the processed background signal into the image signal. The device mainly comprises: a low frequency filtering unit and a gain calibration unit; or the low frequency filtering unit and a compensation processing unit. Making use of the method and the device of the invention can solve a problem that the luminance of outgoing image of a CMOS image sensor is nonuniform, and avoid a phenomenon of appearing FLICKER on the outgoing image.