The present disclosure provides a projection image correcting method and a projection apparatus. The method includes: receiving real-time brightness values of M sub-images in a current to-be-displayed image, the real-time brightness values being acquired by a plurality of sensors arranged on a reflector which is located opposite to a projection lens, and obtaining a brightness adjusting value of a j-th sub-image in the current to-be-displayed image according to the real-time brightness values of the M sub-images. Adjustment is made, in combination with brightness adjusting values obtained from the current image to be displayed, to brightness values of each sub-image in an image to be displayed after the current to-be-displayed image, thereby making brightness of displayed images uniform, and improving the projection image quality.