Abstract: The paper gave steps of fault tree analysis, drew fault tree diagram of mine gas, and made logical analysis for gas accident with FTA method. It found out minimal cut sets and minimal path sets by theory of Boolean algebra law method. It determined importance degree of structure of basic events through solving minimal cut sets and minimal path sets, so as to know degrees of danger and safety of coal mine and combination relation of basic cause events of gas accident and their importance. It also gave prevention measures of gas accident.