Abstract: According to theory of butterfly-shaped plastic zone around roadway in host rockmass,the instantaneously extend mutation characteristics of butterfly-shaped plastic zone were analyzed,a mechanism conjecture of butterfly-mu- tation rockburst in coal seam roadway was then developed. The presented conjecture considered an instantaneously ex- ploration mutation characteristics of butterfly-shaped plastic zone as the main potential cause of roadway rockburst. Further,mechanics essence and physics process of the formation, evolution and occurrence of rockburst were ex- plained. Necessary and sufficient conditions of rockburst were proposed and criterion of roadway rockburst was built. In this fashion,mechanisms of different types of roadway rockburst ( roof burst,floor burst,rib burst,etc. ) can be ex- plained properly. This “conjecture” had the capacity of predicting the unknown phenomenon,which normally associ- ates with from,at least,1 to 4 huge butterfly-shaped plastic zones inevitably occured under a roadway rockburst. In ad- dtion,this “conjecture” could acquire critical index and measurable parameters for risk assessment and prediction.