Abstract: The large-scale experimental apparatus for simulating coal and gas outburst was improved by inserting two gas sensors and two temperature sensors.Then, the coal and gas outburst test was conducted by altering the outburst orifices which are 10 mm, 30 mm, 50 mm separately in diameter.The result show that when the gas pressure was 0.75 MPa, the coal and gas outburst did not occur as the outburst caliber was 10 mm; However, it took place as outburst caliber were 50 mm and 30 mm under same gas pressure and the weight of outburst coal were 25.40 kg and 15.05 kg respectively.It is obvious that the amount of coal goes down with decrease of outburst caliber, so does outburst intensity.Besides, the size of outburst caliber affects outburst condition, namely the outburst distance and destructiveness increases as caliber size adds.Additionally, the proportion of coal particle whose size ranges from 1.6 mm to 5.0 mm declines after outburst, while the one whose size is smaller than 0.75 mm increases, which indicates that strong crushing energy appears during outburst.Moreover, as the outburst caliber increases, coal body tends to failure, leading to coal and gas outburst, and the release of gas in coal is influenced by caliber, which further affects the variation tendency of gas pressure.With the increase of outburst caliber, the decline of gas pressure quickens and crushing effect that gas exerts on coal gets more apparent.In addition, the temperature of coal changes as well during outburst, which can be accounted by the theory that outburst caliber influences failure and outburst characteristics of gassy coal.