Objective:The topographical mapping technique of cortical evoked potential was used to observe the changes of the functional activities in the primary somatosensory area of cortex (SI) during external stimulation,the immanent relation between external stimulation and topographical mapping of cortical somatosensory evoked potential (CSEP). Methods:33 healthy adult volunteers were under observation. Cerebral electric signal processing system was used to lead CSEP on the scalp. The external stimulation was applied as following:①A soft paintbrush was used to slightly brush the face only. ②Paintbrush was used to slightly brush the lower limb only. ③Paintbrush was used to slightly brush the trunk only. ④Paintbrush was used to slightly brush the lower limb or the trunk or the Gallbladder Meridian (GBM) and passing the upper arm by imitating the speed of meridian transmission phenomenon respectively. Results:①Evoking responses appeared in the foot areas in SI,without meridian transmission phenomenon when brushing the face,lower limb or trunk only. ②Healthy volunteers were offered imitation of sensation conduction along the GBM as well as brushing through the upper arm in addition,while,the results showed that the evoking responses appeared in the foot,the upper arm and the face representation area of SI simultaneously. Conclusion:The external stimulation along the meridian course was able to change the distribution of evoking responses in SI during stimulating acupoint. But the local stimulating on face,lower limb or trunk can not change the distribution of CSEP. The results provided experimental evidence for the supposition that 'activation in sequence in periphery'was the decisive factor for the formation of meridian transmission phenomenon.