In the study，the effects of concrete age and stress release of surrounding rocks on the initial support strength and reliability of concrete were investigated. Taking the non-motor vehicle tunnel of baiyangshan as the engineering background，the supporting reliability was calculated and compared. Firstly，considering the influences of stress release of surrounding rock and concrete hardening，the mechanical parameters of surrounding rock and the displacement of monitoring points during excavation process were obtained based on the in-situ monitoring data and BP neural network algorithm. The inversion results were compared to the monitoring data，based on which the variation of stress in surrounding rock was analyzed. Then，the variation of reliability of initial support during excavation was calculated based on the ultimate tensile and compressive formulas of the lining. Test results show that the stress rise of lining mainly occurs in the initial phase after construction，the lowest reliability of lining occurs at the arch waist position in 2-7 days，when the lining is most likely to be destroyed. When considering the effects of stress release and concrete hardening，the reliability will be further lower. This analysis results can provide reference to the safe construction of tunnel.