The entrance portal section of a tunnel is located in toppling deformed ground and is shallowcovered and asymmetricallypressured. Two deformation incidents occurred during the construction of the portal section of the tunnel. In the paper, the causes for the deformation incidents are analyzed, and countermeasures such as muck piling, grouting and additional wiremeshing and shotcreting are taken. In the end, the deformation of the tunnel portal section has been brought under effective control and the possible tunnel collapse and landslide have been avoided. In the construction of the remaining tunnel section, the support parameters have been adjusted and the “threebench eightstep” construction method has been used innovatively. Finally, the tunnel has been completed successfully. 