The overall finite element model of a submerged floating tunnel(SFT) is established using ABAQUS software, and the slacking state of the cable is simulated by changing its stiffness to explore the slackage of the SFT cable and the structural dynamic response under impact load. Subsequently, the hydraulic resistance amplitude corresponding to the vibration velocity of the tube is calculated by the UAMP subroutine, obtaining the impact dynamic response of SFT considering the slackage of the cable. Finally, the effect of impact load, buoyancyweight ratio, and cable inclination on the dynamic response is analyzed. The results reveal the following: (1) Under the impact load, the SFT cable will experience slackage, increasing the structure′s overall dynamic response. (2) During the slackagetension process, impact tension is generated. (3) Increasing the magnitude and duration of the impact load will increase the slackage range, the recovery time, and the impact tension of the SFT cable. (4) Increasing the tube′s buoyancyweight ratio is beneficial to reduce the slackage of the cable, and the recommended buoyancyweight value is 1.4. (5) Considering the slackage effect, initial force, and SFT cable arrangement, the recommended cable inclination angle value is between 45° and 60°.