Abstract: Slag MTC was tested successfully for gas channeling prevention in cementing based on machenism of annular gas channeling. During test,slag MTC exhibited shorter transition time, rapid development of early strength,less post-curing shrinkage of cement column,good compatibility and right angle shaped consistency curve under high pressure and high temperature,attributed to controlled activation speed of slag and development of early strength. During the test in ?117.8mm production casing’s cementing in well Mapeng 2, which has five gas intervals with high pressure,high quality cementing was obtained without any gas channeling observed. It indicates that slag MTC can not only improve bonding quality,but also exhibits high prevention against gas channeling.