The disclosure discloses an apparatus for online volumetrically detecting grain yield based on weight calibration comprising left volumetric granary, right volumetric granary and push board. The left volumetric granary is provided on its bottom with first weighing sensor, and in its side with unload grain port opening and first closing door, the right volumetric granary is provided on its bottom with second weighing sensor, and in its side with unload grain port opening and second closing door, the left volumetric granary and the right volumetric granary are provided on their tops with the push board, the push board is a hollow box structure with a top side and a bottom side both opened, and is slidably mounted to a top of the left volumetric granary and the right volumetric granary through a slide driving mechanism.