Objective To analyze and study the biomechanical model of oblique-pulling manipulation in traditional Chinese medicine for the treatment of lumbar disc disease such as intervertebral disc protrusion, and compare the mechanical properties of two different manipulations, i.e. traditional oblique-pulling manipulation under impulse excitation and improved oblique-pulling manipulation under harmonic excitation. Methods The vertebra was set as rigid body, while the intervertebral disk and surrounding ligaments as viscoelastic body. A vibration system with 5-degree freedom for simulating lumbar L1-L5 was established. The basic vibration equation was solved using analytical method. Results The effect of improved oblique-pulling manipulation was related to the frequency of harmonic excitation. If the frequency of harmonic excitation was not higher than 1, the maximum displacement of the diseased segment under harmonic excitation was larger than that of traditional oblique-pulling manipulation under impulse excitation. With the lesion location shifted downward, the damage ratio (DR) under harmonic excitation was gradually decreased as compare to that under impulse excitation, indicating the safety of the improved oblique-pulling manipulation increasing. Conclusions The curative effect of oblique-pulling manipulation under harmonic excitation at the frequency lower than 1 was better than that of traditional oblique-pulling manipulation under impulse excitation, especially in that the medical injury can be controlled by oblique-pulling manipulation under harmonic excitation at the frequency no higher than 1.