The invention provides a pulsed detonation engine pressure back-propagation suppression structure comprising a loop sleeve and a multi-stage pressure attenuation device; the multi-stage pressure attenuation device comprises a front end attenuator and a back end attenuator, and the middle stage number is adjustable to form a multi-stage adjustable structure; an attenuator reduces back-propagation pressure by expanding a channel; the loop sleeve is used to connect and fix the attenuator; the loop sleeve also forms a resonant cavity and an external flow channel with the attenuator; and incoming flow is divided into the inner and the outer parts through an air-dividing cap, and the resonant cavity communicates with outer air flow through an air inlet groove and communicates with an inner flowchannel of the attenuator through dilute wave holes. According to the pulsed detonation engine pressure back-propagation suppression structure, a plurality of back-propagation pressure decay methods are formed by the ingenious combination of structures; the current back-propagation suppression theory is comprehensively operated, such as bluff body reflection, expansion channel decompression, resonant cavity dissipation, and the like; and the attenuation distance of the back-propagation pressure is short, the attenuation effect of the back-propagation pressure is good, the back-propagation pressure and back-flow gas of a detonation tube can be reliably suppressed, and the good application effect based on a certain incoming flow pressure head is possessed.