In order to avoid the serious safety accidents induced by tunnel rehabilitation/enlargement and improve the safety risk control capacity, the safety risk assessment of collapse of Houci Tunnel is carried out. The safety index system of tunnel rehabilitation/enlargement is established according to the existing research results and the actual situation of the project; and then the correlation degree of each index is determined by matterelement extension model, the entropy weight method is used to calculate the index weight; finally, the probability of the risk and risk severity are evaluated respectively, and the risk grade is identified by the risk matrix. The safety risk assessment method is applied to Houci Tunnel, and the applicable results show that the abovementioned method is feasible for safety risk assessment of tunnel rehabilitation/enlargement.