The invention belongs to the field of consolidating existing building foundation, in particular relates to a method for consolidating the existing building foundation of which the upper structure cannot provide large counter-force. In the method, riprap concrete is adopted as a main material of a pile; holes are dug manually; and block stones or cobbles with the diameter of between 2 and 20cm are thrown into the dug holes in a mechanical or manual mode, and the poured concrete can be compactly filled in gaps generated in a block stone settling path at any time so as to form a compact riprap concrete pile with higher strength. Therefore, the pile end can be placed in a better bearing stratum on the deep part of the foundation, and complete or partial load of a building is transferred to the stratum to fulfill the aims of reducing additional stress of foundation soil under the substrate, reducing settlement and consolidating.