The invention aims to provide a pile casing device for hole formation in building foundation and a construction method of the building foundation by adopting the pile casing device. The pile casing device for hole formation in the building foundation comprises a pile casing body formed by a round steel pipe, and is characterized in that an impact cone is arranged at the bottom end of a pile casing, the lower half part of the impact cone adopts a cone whose diameter is larger than or equal to the outer diameter of the pile casing, the sharp corner of the cone faces downwards, the upper half part adopts a cylinder whose diameter is smaller than the inner diameter of the pile casing, and the upper half part of the impact cone is inserted into the casing body from the bottom end of the pile casing and fixed into a whole in the joint position through welding or casting or bolts. The construction method of the building foundation by adopting the pile casing device comprises construction steps as follows: 1), the pile casing device is used for construction of a pile hole; (2), the pile casing is lifted up to form the pile hole; (3), pile end treatment is performed according to soil property and upper load requirements; and (4) construction of a pile body is performed.