Objective To prevent the recurrence of nitrite poisoning caused by siphonage through a waterpipe siphon， its causes were investigated and analyzed， and prevention and control measures are discussed.Methods A field epidemiological investigation， hygiene investigation， and laboratory testing were used to identify causes and possible sources of contamination in this poisoning event.Results A total of nine cases were found with cyanosis （100.00%）， fatigue （66.67%）， and nausea （55.56%）. The epidemiological curve showed one point source exposure pattern， with an interval of 50 min between the first and last cases and an average incubation period of 20 min. Different concentrations of nitrite were detected in vomit， residual food， and tap water. A negative correlation was observed between nitrite concentration in vomits and diastolic blood pressures （r_s=0.798， P<0.05）. Patient symptoms were significantly relieved after receiving specific treatment for nitrite poisoning.Conclusion This incident was caused by an anticorrosive solution containing nitrite in pickling tanks flowing back into the tap water pipeline through siphonage， which led to tap water contamination and poisoning. The sense of responsibility and standardized management of enterprises are suggested to be strengthened. The water pipe network for production should be separated from that of domestic water and non-return valves should be installed at key locations to avoid similar poisoning events.