To solve the problem of drilling small-diameter deep-hole on difficult-to-cut materials, a kind of DF system combined with low frequency axial vibratory drilling was used. Its vibratory frequency was controlled by a frequency converter and could be adjusted continuously on-line. An inner chip removal deep-hole bit with dimension Φ8.95×500mm was developed and the material of the cutting tip was carbide alloy. Then, the drilling experiment of small-diameter deep-hole on the difficult-to-cut materials 1Cr11Ni4NMo was done. It can be found in the experiment that the chip remove was smooth, the cutting force was little, the cutting tool wear was light, the process of drilling was stable, and many factors of interfering roughness could be canceled or lightened effectively. The results show that DF vibratory drilling system can improve the machining precision and increase efficiency.