This paper presents the rehabilitation project of Dabanshan highland road tunnel. Cause analysis is carried by insight into the information of climate, geological, hydrological condition, tunnel defects type and parameters. Water leakage, low temperature and poor rock condition are considered to be source of tunnel defects, and the essential of rehabilitation of highland road tunnel are water leakage treatment and heat preservation system reinstatement. Measures taken to solve the problems of cracks, water leakage and frost are introduced in detail, and results show that measures taken are proved to be effective. Knowledge and experience gained are helpful for similar projects in future.