Abstract: In order to investigate the dynamic responses of a coupled tunnel system with large span and small clear distance under the blasting load generated by the construction, a 3D finite element numerical model for dynamic responses analysis of excavating a transverse passage from a constructing tunnel to an existing tunnel under the equivalent blasting load is established.The law for the dynamic responses of the existing tunnel is analyzed, and the threshold value of the safe distance between blasting surface of the transverse passage and the existing tunnel is determined under the current construction parameters.The results show that the main affected area of the lining lies at the lower arch waist that faces the blasting directly, where both the maximum vibration velocity and the maximum tensile stress appear.The horizontally radial vibration velocity(along the axis of the transverse passage)makes the main contribution to the overall vibration velocity of the lining.Therefore, the monitoring data of the horizontal vibration velocity at this position can be treated as the evaluation indicator for assessing the influences induced by the blasting construction of the transverse passage.The distributed law and varying trend of the dynamic stress of the existed tunnel lining are similar to the vibration velocity, showing a satisfied positive linear correlation between them.There is a negative power exponential relationship between the peak vibration velocity of the existing tunnel lining and the distance from the excavation face of the transverse passage.In order to avoid the unfavorable influences on the safety of the lining structure, the current parameters of the blasting construction are suggested to be optimized when the distance between the excavation face of the transverse passage to the existing tunnel reaches 10 m.