A bit assembly includes a bit for driving a screw, a shank for holding and driving the bit to rotate about a pivot axis wherein the bit is capable of moving relative to the shank in a predetermined range, and a limiting structure formed between the bit and the shank for preventing the bit to move beyond the predetermined range. The bit and the shank are made of different materials and form a sliding connection so that they have a certain buffer space in the axial direction and in the circumferential direction thereby reducing the effect of impacts on the service life of the bit assembly.