For reducing or avoiding the iatrogenic nerve function injury due to the excessive retraction for a nerve root during a spine surgery, a silicon piezoresistive pressure sensor was employed in the nerve root retractor to quantitate the retraction for the nerve root and to improve the performance of spine surgery. To measure the pressure exerted upon the retracted nerve root, a pressure sensor was adhered to the nerve engagement surface of a nerve retractor. The rabbit and goat experiments were performed on nerve root retraction by different time durations and pressure extendings,while the nerve function injury was assessed by monitoring the electromyogram responses. Experiments show when the increase of average pressure is about 14 kPa, the change rates of latency and amplitude are 112% and 21.21%, respectively, which reveals that the retracted nerve root axonal is damaged. Furthermore, loading similar average pressare, the more the retraction time applies to the nerve root, the worse the nerve function is hurt. In conclusion, the relationship between the pressure exerted on the nerve root and the corresponding neuromuscular responses has been founded via the results of animal experiments, which shows the degree of nerve root impairment is positively correlated with the duration and extent of nerve root retraction, and can be used in the study of retraction threshold values.