Embodiments of the present invention are a high dynamic range (HDR) synthesis method and apparatus, an image processing chip and an aerial camera. The method includes: acquiring a plurality of to-be-synthesized images having different exposure time; calculating a mean brightness of the to-be-synthesized images; determining an image brightness type of the to-be-synthesized images according to the mean brightness; calculating a brightness difference between adjacent pixel points in one to-be-synthesized image; calculating an inter-frame difference of different to-be-synthesized images at a same pixel point position according to the brightness difference; determining a motion state of the to-be-synthesized images at the pixel point position according to the inter-frame difference; and weighting and synthesizing the to-be-synthesized images into a corresponding HDR image according to the image brightness type and the motion state.