In order to understand the influence mechanism of grouting pressure fluctuations on pipe joints in large cross-section rectangular pipe jacking, this paper relies on a large cross-section rectangular pipe jacking project in Nanjing, and uses research metho-ds such as theoretical analysis, engineering analogy, and numerical simulation to investigate the influence mechanism of grouting pressure fluctuations on the stress state of large cross-section rectangular pipe joint structures under local pressure suppression condit. The external loads of large cross-section rectangular pipe joints was calculated, and the concrete damage plasticity model built-in ABAQUS software was used for numerical modeling to study the damage evolution mechanism of reinforced concrete pipe joints under different grouting pressures. The results show that: (1) grouting load, as a variable load, has a significant impact on the stress distribution of the pipe joint, such that the grouting pressure should be included in the design of the pipe joint; (2) For this project, the theoretical grouting pressure is 0.311 MPa. In view of the need to suppress the carrying-soil effect, the grouting pressure should be appropriately increased, but it must be controlled within a reasonable range; and (3) From the perspective of damage evolution, when the grouting load reaches 0.6 MPa, the tensile damage to the top plate of the pipe joint has reached a high level. Therefore, 0.6 MPa is used as the grouting pressure warning indicator for this project, while 0.9 MPa should be used as a control indicator for grouting pressure.