Abstract: In the case of a tunnel fire, heat release rate is an important parameter for evaluating the critical velocity, the maximum temperature and the temperature distribution. In a tunnel, fire source height and tunnel width are two key factors which affect the growth of the heat release rate. To evaluate the influence of the two factors on fire growth, a series of tests were conducted in a 1:10 scale tunnel, and the burning process of pool fire was studied. Results show that the burning rate of tunnel fire is significantly larger than the one in open space, and tunnel fire can be divided to three stages:initial stage, transition stage and stable burning stage. When changing the fire source height, the mass burning rate of ground fire (the ration of fire source height to tunnel height, H^*=0.1) was far less than other situations. For a fire of H^*=0.7, the mass burning rate became 3.53~5 times as big as that of the ground fire. The dimensionless total flame extension length is proportional to 2/5 power of dimensionless heat release rate, and the coefficient is less than Hasemi's model due to the restriction of tunnel wall.