Gas evolution behavior in slow pyrolysis of 14 different coals at 3 K/min under nitrogen atmosphere has been investigated. The overall yield of volatile matter is consistently lower than that measured using the standard proximate analysis test, and evolution rates of pyrolyzed gases were dependent on temperature level. The formations of CO and H₂ above about 800℃ are considered as a result of carbon-steam gasification together with thermat decomposition of coal. The composition of hydrogen and hydrocarbon gases other than methane increased with the value of VM（daf） of coal, while the amount of CO evolved increased with the value of O(daf) of coal.