The invention relates to the field of treatment of building foundations, in particular to a construction method of a T-shaped pile and a T-shaped drilling tool for construction of the T-shaped cast pile. The construction method of the T-shaped pile comprises the steps that a large-torque slewing drilling machine, namely a construction machine, is adopted and is mounted through conventional processes including moving in place, centering and leveling; a large-section pile cap hole is formed through an auger bit; after the large-section pile cap hole is formed, the auger bit is located in the original position and is in a static state, and a drill rod continues to rotate to downwards push a squeezing and expanding drilling tool, so that a pile rod hole for a small-section pile body is formed; the rotary drilling procedure is conducted, a threaded bit is made to protrude towards the outer side of the auger bit, and pile lateral threads are rolled on the pile rod hole for the small-section pile body in a negative angle tangency point direction; and redundant soil of the compaction-thread T-shaped drilling tool and a pile cap is rotatably lifted to the ground. The construction method and the T-shaped drilling tool can improve the bearing capacity of a pile foundation and have the advantages that labor and time are saved, and the efficiency is high.