The deformation of tunnel roof could be regarded as a process of energy accumulation，and tunnel roof will collapse suddenly when the total potential reach the critical value.According to functional catastrophe theory and upper bound theorem，a reliable failure pattern based on Hoek-Brown failure criterion was established，and the effect of river was considered.By using the boundary conditions and geometric conditions，the functions of detaching curve and the supporting pressure were derived.At last，the supporting pressures of two different sections of Sunanshan tunnel in Louheng highway were calculated in this method，respectively，and the results were compared with the monitoring data，which shows the validity of this way.
