Due to a triple perforating explosion, the wellbore annulus may experience the pressure fluctuations, potentially causing safety incidents such as channeling and disconnection of the perforating string. A prediction model for the pressure fluctuation in the wellbore annulus during the perforation explosion is established for a typical perforating gun-packer-casing structure. This model is based on fluid-structure coupling theory and theoretical research into pressure fluctuations. The study investigates the distribution of pressure fluctuations and their impact in typical triple-operation ultra-deep wells, taking into account factors such as the initial annular pressure, explosive mass, and type of explosive on the complete wellbore annulus pressure (below the packer). The obtained results indicate that the increased initial wellbore pressure and the increased explosive mass can lead to a higher peak in pressure fluctuation at the wellbore annulus, particularly when the initial wellbore pressure ranges from 50 to 125 MPa, and the explosive mass ranges from 15 to 40 g. Among various explosives such as TNT, HNS, RDX and HMX, RDX has the largest peak pressure fluctuation at the wellbore annulus when the explosive mass is the same. Therefore, the selection of HNS and HMX explosives, along with reduction in the initial wellbore pressure and the explosive mass, can significantly lower the risk of perforating string failure. The results provide reference for annulus pressure evaluation of triple perforating work.