Abstract: During construction, a huge collapse occurred between the down lines from K225 to K283 of the Fengyakou tunnel of Yuanmo highway in Yunnan Province. This paper analyses the reasons for the cause of the huge collapse. It is found that the collapse was due to the section located at a fault zone with rich groundwater and slurry often gushing. The paper provides the treatment measures including surface treating, underground treating and drainage in the collapsed tunnel. Monitored results showed that e the stress and deformation of the preliminary bracing and second lining of the tunnel cross section had no change, which indicate that the force and deformation were becoming stable, and the change was with in the limits. The monitored results also showed that the treatments were not only reliable in theory, but also sound in practice, and can be a good guide and reference for the treatment of similar highway tunnel collapses.