The invention relates to a construction method for an in-situ water-injection pure soil compaction pile composite foundation. The construction method mainly comprises the steps of site clearing and flattening; surveying and setting out; construction equipment assembling in-position; hole guiding; water injection for humidifying; pipe pulling for secondary punching; falling-back soil bottom tamping; padding humidifying; hole interior layering padding, compaction tamping and hole forming; top loosened layer removing; and spreading and compaction. Through the construction method, the composite foundation can be formed, and the construction method has the advantages that construction machines are saved, the construction cost is reduced, the working efficiency is improved, noise and muddy waterpollution are reduced, residue soil is removed, and the environment is protected.