In this paper, the decomposition of pure CO2 into CO and O-2 were carried out in a segmented electrode DBD micro-plasma reactor at ambient pressure. With the assistance of gas chromatography, the influence of key factors like electrode interval and barrier thickness on the DBD filamentary behavior and CO2 decomposition process were investigated systematically. Meanwhile, the detailed electrical characterization during discharge process was also performed. The results indicated that a relatively higher CO2 conversion and energy efficiency could be obtained at the propitious condition of longer interval between adjacent electrodes and smaller barrier thickness, and the highest CO2 conversion and corresponding energy efficiency are 16.9% and 3.6%, respectively, at the condition of an applied voltage of 18 kV and 1.0 mm barrier thickness. Longer electrode interval can result in an increase in plasma density as well as enhance fringe effect. While the smaller barrier thickness, the smaller corresponding gas breakdown voltage, which meant that more electrical power was used for gas excitation. Accordingly, more energetic electrons were generated and more collisions between the electrons and CO2 molecules occurred. These were considered to be main reasons for enhanced CO2 decomposition process.