This study investigated the effects of high hydrostatic pressure (HHP) treatment on the physicochemical properties and microstructure of frozen pea protein gels and elucidated the underlying gelation mechanisms. Heat-induced pea protein gels were subjected to three HHP conditions (100, 300, and 600 MPa for 15 min each) and evaluated in terms of their color, textural attributes, solubility, and subunit composition before and after freezing. Compared with the native pea protein isolate (PPI), HHP-treated gels demonstrated significantly reduced gel hardness, which gradually declined as pressure increased. Dynamic rheological analysis revealed that HHP-treated gels exhibited enhanced elasticity and viscosity, accompanied with a dense and highly homogeneous network structure. The subunit composition involved in gel formation changed notably after HHP treatment, and the number of participating proteins and the content of free sulfhydryl groups decreased with increasing pressure (100 MPa<300 MPa<PPI<600 MPa). The water-holding capacity of HHP-treated gels improved, following the trend of 600 MPa>100 MPa>PPI>300 MPa. Dynamic rheological results further confirmed that in all samples, the storage modulus exceeded the loss modulus, indicating a predominantly elastic gel network. Freezing disrupted the gel structure under all treatments, reducing surface smoothness, and gel hardness before and after freezing decreased progressively with increasing pressure. Soluble protein content followed the order of 100 MPa<300 MPa<PPI<600 MPa. After freezing, the total thiol content at 100 MPa increased by 0.60%, suggesting increased protein participation in gel formation and extensive disulfide bond formation at this pressure. Water distribution and differential scanning calorimetry analyses demonstrated that ice crystal formation at 100 MPa caused minimal structural damage, with only slight alterations in water distribution. The enthalpy change in the HHP-treated gels had decreased significantly compared with that in the control, as follows: 3.54% at 100 MPa, 1.79% at 300 MPa, and 9.46% at 600 MPa. In summary, among gels, the pea protein gel treated at 100 MPa for 15 min had the best freeze resistance. HHP treatment effectively modulates the gelation mechanism of pea protein, promoting the formation of a fine and compact gel network. It also mitigated structural degradation after freezing and enhances the freeze-thaw stability of pea protein gels. These findings provide valuable insights into the application of HHP for the structural modification of plant proteins and the development of high-quality frozen food products.