In view of the phenomenon that the affected area is broader, more severe losses and more difficult to relief in the urban agglomeration after major natural disasters,it is proposed that transport system reliability calculation method which based on BP neural network model.First of all,analyze the urban transport system network after a disaster, using the weight contribution rate analysis method to extract the key nodes in the network; Second, re-integrating the extracted nodes and establishing a new road network model which based on BP neural network;Then, using the cut set algorithm computing network reliability, and combined with the extent of damage of the road network after a disaster, putting forward the calculation method of urban agglomeration road network reliability after disasters; Finally, for example as changsha-zhuzhou-xiangtan urban agglomeration, examining the authenticity of the method.