The crown top settlement and convergence deformation of trilane tunnel at Wanggangshan Tunnel Portal are fast and large by CRD method and bench method; the crown top settlement and convergence deformation rate reaches 35 mm/d, the daily maximum settlement and convergence reach 4.7 mm and 4.8 mm, respectively; the 15day accumulated settlement and convergence reach 109 mm and 53 mm, respectively; and the deformation is still developing. Hence, site investigation is carried out. The analytical results show that the main causes for large deformation are shallow burry, large span, low flattening rate and mixed zone of diabase intrusive rock and sedimentary rock which is broken weak and slippery. The optimization of the construction scheme is put forward, including using doubleside drift method, advanced support and primary support optimization and detailed construction sequence. The monitoring results show that the deformation of the surrounding rock has been effectively controlled, good primary support effect has been achieved, the crown top settlement and convergence have been effectively controlled, and the tunnel safety has been guaranteed.