Because of the special structure, the rotary drilling rig is not suitable for small diameter bored piles. Aiming at this problem, a new technology of rotary holing for small diameter bored pile has been developed, which contains the self-designed XFK600 non-dilated bit, special technological parameters and mud protecting by tube with steel liner. This technology has been widely used in many large projects after successful experimental study. The paper introduces the technical innovation, key technologies and application effects.