Abstract: The response spectrum theory widely applied in earthquake engineering was employed to investigate blasting seismic wave induced by controlled blasting with precise delay time interval.The similar model test of slope excavation was designed and carried out.The influence of different millisecond delay to response spectrum property was analyzed.Considering the interaction between intensive modes，the modal combination was conducted combined with method of second item combination completely (CQC) to obtain total effect value of structural response.The results shows that，the response spectrum curves of controlled blasting with short millisecond delay have multiple distinct peak points，and the corresponding period is usually within a narrow range of a few milliseconds.With the increase of milliseconds delay between blasting holes，the natural frequency corresponding to response spectrum peak gradually close to the natural frequency of structures，which is detrimental to the safety of the structure.Choosing of reasonable delay time interval should comprehensively consider blasting vibration intensity，blasting effect of rock mass and dynamic response of construction.Under experimental conditions，the reasonable delay time interval between blasting holes is 2 ms.

Key words: Slope, Blasting vibration, Response spectrum, Modal combination, Method of CQC, Delay time interval