The research of combined operation system of automobile gas heater and LNG engine can solve the problem of starting difficulty of the heavy truck using LNG. The stability of the combined operation and the effect of the combined operation on the cold starting performance of the LNG engine were studied through the combined operation tests. The experimental results showed that the automobile gas heater started smoothly and burned stably, and the cold starting performance of the LNG engine was improved significantly through the heating of the cooling liquid by the automobile gas heater. Therefore, adopting combined operation can improve the starting performance of the LNG engine in cold area effectively. 