Abstract： To reveal the propagation characteristics of blasting vibrations induced by blasting demolition of a reinforced concrete support beam in a deep foundation support system，the vibration velocities and frequencies in the horizontal and vertical directions of the support system and the response spectrum characteristic of the enclosure structure of the foundation pit are analyzed based on the monitored vibration data． The vibration test lines were laid in the same and the upper layer to the support beam． The results show that the vibration velocity decays rapidly with the increase of distance． The peak vibration velocity at the blasting layer is 5 ～ 7 times than that of the upper layer within 50 m of the blasting area． However，the peak vibration velocity of the blasting layer gradually attenuates to 1 ～ 2 times than that of the upper layer outside 50 m of blasting area． Besides，there are obvious differences among the components of vibration velocities in three directions in the blasting layer． The radial component has the largest peak value， which is 2 ～ 5 times of the vertical component． On the contrary，the three components of vibration velocities in the non-blasting layer are close to each other． Meanwhile，it is high frequency vibration in the support beam，and the vi- bration frequency of the blasting layer is slightly smaller than that of the non-blasting layer，and both of them have a steep increase phenomenon in the supporting structure of the foundation pit． When the support beam is demolished by blasting，the short-period response spectrum of the enclosure structure of the foundation pit is obviously beyond the designed spectrum，and the blasting vibrations will have a certain influence on the enclosure structure． The related results can provide references for the design of blasting demolition of support beams，vibration control，and the dynamic response analysis of enclosure structure of a deep foundation pit．