An analysis of four series of metro carriage fire tests in different scales was carried out. These metro carriage fire tests including 1:10 model scale tests, 1:3 model scale tests, 1/3 carriage section carriage tests and full scale tunnel tests. The correlation between different scales of carriage fire tests is carefully investigated. The mechanism of fire development is very similar in different scales of tests involving fully developed. A critical fire spread is identified as the key parameter to a fully developed carriage fire and is related to a minimum heat release rate. After the critical fire spread, the fire travels along the carriage at an approximately constant speed. The maximum heat release rate obtained for a fully developed fire is dependent on the ventilation conditions and also the type and configuration of the fuels, and a simple equation has been proposed to estimate the maximum heat release rate. Good agreement has also been found between different scales of maximum gas temperature, gas concentration and extinction coefficient. The heat fluxes from the flames could be slightly overestimated in model scales.