Neural system generates various kinds of fire patterns when stimulated by external or internal inputs. Acupuncture, as a mechanical action, is equivalent to an external stimulus to the neural system. When stimulated by the acupuncture, the neural system can evoke irregular electrical signals. Neural system is a complex nonlinear dynamic system that possesses strong nonlinear characteristic, so it is necessary to introduce the nonlinear time series analysis method to study the neural electrical signal. In this paper, an experiment is designed in which acupuncture is made at Zusanli with four different acupuncture manipulations to obtain action potentials on dorsal spinal nerve root. The concept of the interspike interval (ISI) is used for the study of the acupuncture electrical signals. Several nonlinear characteristic parameters are extracted, such as the Lyapunov exponent, correlation dimension and Lempel-Ziv complexity, and the neural coding of the electrical signal evoked by different acupuncture manipulations is obtained. It is also shown that under the effect of the acupuncture, the electrical signals of dorsal spinal nerve root based on acupuncture at Zusanli point has distinguished chaotic features.