Asphyxia typically occurs due to oxygen deficiency in confined spaces. A male researcher died in a minor car accident. He had loaded a container filled with liquid nitrogen in his car the day before the accident. Clinical analysis of blood showed that blood alcohol concentration(BAC), carboxyhemoglobin (CO-Hb), drugs and toxins were negative. During the car investigation, it was found that there was frost around the lid of the liquid nitrogen container with a trace amount of liquid nitrogen left. To determine the cause of death, the simulation test was performed by reconstructing the situation of liquid nitrogen leaking in a confined space. The results showed that liquid nitrogen in the container was continuously evaporated and reduced the oxygen concentration in the car. After 20 min the state of oxygen deficiency was reached and then the oxygen concentration was cut down to 6.5 % within 10 hours. It was concluded that the cause of death was oxygen-deficient circumstance resulted from the evaporation of liquid nitrogen in the car. In order to determine the cause of death, it is necessary to perform a simulation test considering all potential factors that may affect the accident.