A projection system (100, 200), comprising a signal processor (130), a light source (111), an optical relay system (112), an adjusting component (150, 250), and a DMD. The signal processor (130) receives image data, the image data comprising a plurality of gray-scale values, wherein each gray-scale value corresponds to a pixel, and the signal processor (130) increases gray-scale values of a plurality of pixels of the image data. The light source (111) is used for emitting illumination light, and the optical relay system (112) provides the illumination light to the DMD so that the DMD can modulate the illumination light to obtain projection light required for projection of an image. The adjusting component (150, 250) reduces the luminous flux of the illumination light of the DMD when the gray-scale values of the plurality of pixels of the image data are increased, and the proportion of reduction of the luminous flux of the illumination light is adapted to the proportion of increase of the gray-scale values of the image data. The DMD modulates the adjusted illumination light according to the image data with increased gray-scale values to produce the projection light required for projection of the image. Also disclosed is a projection method. The projection system (100, 200) has higher contrast.