Cross-section-variable drilling tool for cement mixing pile

The invention relates to a cross-section-variable drilling tool for a cement mixing pile. The cross-section-variable drilling tool comprises an outer drill rod and an inner drill rod which are concentrically and coaxially arranged, a conveying pipe is arranged in the inner drill rod, outer drill rod blades are arranged on the lower portion of the outer drill rod, a spraying rod is connected to theend of the inner drill rod through a flange board, an inner drill bit is connected to the lower portion of the spraying rod through a flange board, a jet pipe is installed on the upper portion of thespraying rod, inner drill rod blades are installed on the lower portion of the spraying rod, one end of the jet pipe is hermetically connected with a conveying pipe for conveying a jet medium, jet orifices are formed in the other two ends of the jet pipe respectively, each of the outer drill rod blades and the inner drill rod blades comprises a fixed blade and a movable blade, the movable bladesare slidably connected with