The basic idea of New Austrian Tunneling Method is to employ the self-sustaining ability of surrounding rock，and the bolt plus shotcrete system is one of the key technologies. Controversies still exist over the function of bolts and how to reasonably consider their effect. This paper presents an elastic-plastic bolt element and performs numerical simulation of tunnels in loess with bolt elements. The reasonable length of bolts and equivalent increase in values of parameters for surrounding soils are suggested for actual design of tunnel.