Coal char combustion under the O-2/CO2 atmosphere is one of the prospect cleaner coal technologies, its combustion characteristics and dynamics research are the foundations of project application. In this paper, the results of a study on the combustion characteristics of three coal chars (Liupanshui lignite, Zhungeer bituminous, Qinhuangdao anthracite) under different oxygen volume content (21%, 25%, 30%, 35%) are presented by TGA, the effect of oxygen volume content to coal-char reaction were analyzed. Simultaneously classical dynamics and time effect fractal dynamics had carried on the analysis separately to the coal char combustion. The results showed that, with higher the oxygen content, the lower the ignition, burnout temperatures are, the char combustion time shorten, activation energy reduces slightly whether use classical dynamics or time effect dynamics analysis, and the activation energy obtained by the former is smaller than the latter.