The RG1 tunnel on the right wing of the Gulward Dam body, located in the city of Neka, Mazandaran province, is designed to access the dam crest with a length of approximately 600 meters. To investigate the stability of the RG1 tunnel, general geological studies, engineering geology and rock mechanics studies have been carried out based on the strength parameters of the rock and rock masses in three sections. These studies include the investigation of geological characteristics, rock mass classification, rock mass strength parameters, RMR and Q classification systems. Numerical analysis of the RG1 tunnel section in different rock classes is presented using Phase2 software. Also, temporary rock retention systems have been modeled and analyzed for different models. The results show that in limestone mass, shotcrete with a thickness of 50 to 100 mm does not require a bolting process for tunnel wall stability, but in shotcrete with a thickness of 100-150 mm with wire mesh, 5 complete bolts are required in the wall and tunnel crown.