The invention discloses a construction method of a building cast-in-situ bored pile. The construction method comprises the steps of drilling in advance, cleaning, burying a shield-tube, preparing mud, drilling by using a machine and discharging the residue of the mud in a circulating way, reaming, performing borehole cleaning, making and placing a steel reinforcement cage, and pouring concrete. According to the construction method, geological conditions can be known before filling the pile by means of drilling in advance, and whether the geological conditions meet construction conditions or not can be determined, so that the type of a drilling machine is more easily determined in advance, and the construction efficiency and project quality are improved; the drilling machine and components and indexes of the mud are selected according to the geological conditions, so that the construction efficiency is very high, a great deal of manpower is saved, and construction is safe; the steel reinforcement cage adopts a triangular reinforcement frame and a concrete base, so that the strength and stability of the steel reinforcement cage are improved; therefore, the construction method of the building cast-in-situ bored pile has the advantages of high safety, environment friendliness, high efficiency and wide application scope. The building cast-in-situ bored pile has the advantages of being high in supporting strength and high in quality.