Fibroblast activation protein (FAP) is expressed in more than 90% of tumor-associated fibroblasts in epithelial cancers, providing an excellent target for nuclear medicine diagnostics and therapy. Given the high cost of PET-CT, developing SPECT probes targeting FAP is necessary. A novel FAP inhibitor derived from UAMC1110 was synthesized and conjugated to DOTA via PEG chains. This resulted in a series of inhibitors with good targeting specificity, tumor uptake, and pharmacokinetics. In this study, UAMC1110 derivatives were used as FAP-targeting pharmacophores; PEG chains of varying lengths were employed for pharmacokinetic modification, and HYNIC was used as a bifunctional chelator. The derivatives were labeled with 99mTc using different coligand combinations to explore how PEG chain length and coligand composition affect the in vivo and in vitro properties of 99mTc-labeled FAPI. Four UAMC1110 derivatives (P4, P6, P8, P12) with different PEG chain lengths were synthesized, and a series of hydrophilic 99mTc complexes were prepared. Stability and specificity studies demonstrated that these complexes exhibited good in vitro and in vivo stability and FAP-targeting specificity. In micro-SPECT imaging, these tracers showed rapid tumor accumulation, with 99mTc-TE-P12 and 99mTc-TT-P12 showing promising tumor uptake, low nontarget organ uptake, and high T/NT ratios, indicating potential as SPECT probes.