In tunnel construction, overbreak backfill material has great influence on the distribution of the internal force of the tunnel lining. In the paper, the tunnel excavation is simulated on basis of FLAC 3D finite difference numerical software and the influence of different backfill materials on the bending moment and displacement of the lining structure is analyzed by changing the elastic modulus and the backfill layer thickness. The impact of different surrounding rock grades on the bending moment of the lining structure is also compared. The results show that the maximum bending moment of the crown, sidewall and floor slab decreases as the elastic modulus increases, and it decreases dramatically at first and starts faster and smaller, and tends to decrease gently in the end; the maximum bending moment of the crown, sidewall and floor slab increases almost in linear as the thickness of the backfill layer increases; The maximum displacement of the crown and floor slab increases as the elastic modulus increases, however, the maximum displacement of the sidewall is just on the contrary; The maximum displacement of the crown and sidewall increases as the thickness of the backfill layer increases, however, the maximum displacement of the floor slab remains almost stable.