To further improve the gas separation performance of membrane materials, this study developed a diamine monomer,2-(3,6-bis(4-amino-3-hydroxyphenoxy)-9H-xanthen-9-yl)benzoic acid (BAHXBA), capable of undergoing both thermal rearrangement and crosslinking reactions simultaneously. Subsequently, this monomer was polymerized with six equimolar dianhydride monomers, namely 3, 3′, 4, 4′-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4, 4′-( 4, 4′-isopropylidenediphenoxy) diphthalic anhydride ( BPADA), 3, 3′, 4, 4′-diphenyl ether tetracarboxylic dianhydride ( ODPA ), and 1, 2, 3, 4-cyclobutanetetracarboxylic dianhydride ( CBDA ). Crosslinkable polyimide ( PI) membranes were prepared via thermal imidization, followed by heat treatment at 450 ℃ to yield the corresponding thermal rearrangement (TR) membranes. The experimental results demonstrate that all six PI membranes exhibit excellent mechanical and thermal properties, with glass transition temperatures ranging from 297 ℃ to 336 ℃. Owing to the occurrence of thermal rearrangement and decarboxylation crosslinking reactions, the mechanical properties of the TR membranes decrease significantly, while their gas permeability is substantially enhanced. In particular, the TR membrane derived from BAHXBA and 6FDA monomers display permeability coefficients of 966.32 barrer, 873.33 barrer,265.72 barrer and 41.62 barrer for H₂,CO₂,O₂ and N₂ , respectively. Meanwhile, the ideal selectivity of CO₂/N₂ reaches 20.99, which is close to the Robeson upper bound reported in 2008, and the ideal O₂/N₂ selectivity is 6.39, approaching the upper limit published in 2015. Therefore, the synergistic effect of thermal rearrangement and crosslinking could effectively improve the gas separation performance of membrane materials.