The invention provides a coal seam floor damaged zone depth determination method based on an improved rupture mechanical model and belongs to the technical fields of three under-one above mining and gas extraction. The coal seam floor damaged zone depth determination method is provided on the basis of accurately-measured data of national mines so that the limitation of regions is overcome; the coal seam floor damaged zone depth determination method can completely consider factors which are well-known and influence the damaged zone depth, and consider the influences on the damaged zone depth of a floor by a coal seam inclined angle for the first time, so that the precision and stability of a calculation model are effectively improved.