Objective To investigate the effects and possible mechanism of the local content changes of nitrogen monoxidum on bile reflux in rats’ pylori stress ulcer. Methods Fifty adult SD rats were restrained in planes and then were soaked in cold water to make stress ulcer. They were divided into three groups randomly: the stress group (30 cases), the L-NAME group (10 cases), whose pylori were injected with L-NAME solution and the normal saline group (10 cases), whose pylori were treated with saline solution. Besides, there were another 10 rats taken as the control group. The gastric ulcer index, pH value and bile acid concentration of gastric juice in each group were measured before and after stress. The local concentrations of nitrogen monoxidum in rats’ pylori were also measured by nitrogen monoxidum Biochemical Detection Kit. Results The local content of nitrogen monoxidum in rats’ pylori increased to maximum at 1 h after stress （P＜0.01）, while the bile acid and pH value of gastric juice went up to the maximum at 2 h after stress （P＜0.01）. The ulcer index reached the peak value at 4 h after stress （P＜0.01）. The bile acid concentration and ulcer index of the group injected with L-NAME solution in rats’ pylori decreased significantly compared with those of the group treated with normal saline solution (P＜0.01). The local concentration of nitrogen monoxidum also decreased significantly in the L-NAME group (P＜0.05）. However, there was no difference on pH values of gastric juice between those two groups (Pgt;0.05). Conclusion There is a positive correlation between the local concentration of nitrogen monoxidum in pylori and bile acid in the stomach in rats with stress ulcer. Injection of L-NAME solution in rats’ pylori may reduce the local content of nitrogen monoxidum so that the pyloric sphincter become less tense, which may lead to the significant decreases of ulcer index and bile acid in the stomach. Thus, L-NAME may protect gastric mucus effectively.