Abstract: The investigation process of a car fire accident while driving was introduced. The fire propagation and cause were analyzed comprehensively by means of fire scene examination, interviews and identification of material evidence, and the possible fire causes of electrostatic failure，lightning, spontaneous combustion and arson were excluded. The evidence chain is formed by the fire cause analyses and the witness testimony to result in the fire cause of the oil pipe leaking in the engine compartment and catching fire when encountered electric spark. The accident reason and investigation experience were also put forward.

Key words: fire, car, fire investigation, oil leakage