When excavating a tunnel in a gently sloping strata,serious overcut and undercut problems occur in various parts of tunnel blasting construction due to the existence of horizontal weak interlayer.Based on the project of Baoanying tunnel of Chengdu-Kunming Railway which passes through horizontal sand-shale interlayers,LS-DYNA software is used to simulate the blasting effect with different layer thicknesses to propose reasonable blasting control parameters.And the reliability of the parameters is verified by field blasting tests.The main research results are as follows: (1)When blasting excavation in a horizontal rock layer,the damage range of rock mass along the horizontal direction is large with long cracks,especially at the junction of sandstone and shale.On the contrary,the damage range along the vertical direction,with a small explosive energy utilization rate.(2)The blasting effect of horizontal sand-shale interlayered surrounding rock is significantly affected by hole spacing and the thickness of soft shale.When the thickness of shale interlayer is thin,smaller hole spacing should be selected.With the increase of the shale interlayer thickness,the controllable cracks can be effectively generated by arranging the hole spacing and empty holes to achieve a better smooth blasting effect.(3)The optimal hole spacing of the surrounding rock blasting with different thickness of sand-shale interlayer is determined.When the shale thickness is 5 cm,10 cm,15 cm,20 cm and 30 cm,the optimal hole spacing is 42 cm,46 cm,50 cm and 54cm,respectively.At the same time,the position of the blast hole must be strictly controlled to reduce the blasting vibration as much as possible.