The technical condition of the civil structure of the tunnel is deteriorating, so it is necessary to monitor the invert structure of the tunnel for a long time, so as to find and eliminate the hidden dangers of road traffic in time. The research on tunnel deformation monitoring technology has been carried out at home and abroad, but the research on using distributed optical fiber to monitor the invert of expansive rock tunnel is still few. In view of this, this paper establishes an invert monitoring system based on distributed optical fiber in expanded rock tunnel to monitor the stress characteristics of the surrounding rock of the tunnel basement, so as to timely discover the hidden dangers of road traffic safety.