Abstract: Objective To calculate the liquid nitrogen leakage rate in specific laboratory,and to demonstrate preventive measures against asphyxia. Methods The velocity model of gas leakage was used to show the consequence(suffocation risk) of nitrogen leakage in the laboratory. Results It is simulated that nitrogen will reach 84% at 503.195 s after leakage,90% at 1 006.36 s and 100% at 1 845 s,respectively. Under this emergency condition,the ventilation models,the alarm-limits setting of gas detection devices and the installation location of safety facilities were present. Conclusion To prevent asphyxiation incidents in the work area involving nitrogen,the targeted countermeasures were given,including improvement of safety management system and laboratory operating procedures.