The invention discloses a building shadow extraction processing method for a sentinel 2A image, and the method comprises the steps of S1, extracting the main ground feature component of an urban area,designing a shadow enhancement index based on a sentinel 2A original spectrum to enhance a building shadow; calculating a normalized difference water body index to enhance the water body; extractingan original spectral band Band 8 of the sentinel 2A to enhance other dark reflectivity ground objects; S2, based on the three extracted characteristic components, constructing a combined shadow indexto highlight a building shadow; and selecting an optimal threshold value by using an OTSU method to obtain a final urban building shadow distribution map. By the adoption of the technical scheme, thedifference between the shadow and other ground objects can be remarkably increased, the phenomenon that urban building shadow, water and dark reflectivity ground objects are mixed is effectively avoided, and the extraction precision of the urban building shadow is improved.