The acoustic isolator between the drilling bit and the acoustic piezoelectric transducer can attenuate the drilling noise transmitted through the drill collar to avoid interference with the transmission of acoustic signals while drilling, and also can be used to weaken the influence of downlink acoustic signal with the uplink channel produced by the transducer. This paper improves the characteristic analysis of tapered acoustic transmission model, and the size and structure of the acoustic isolator has been designed which has the characteristic frequencies of 700~800Hz and 1200~1300Hz.