PMSA (prostate-specific membrane antigen) is currently the most significant target for diagnosing and treating PCa (prostate cancer). Herein, we reported a series 68 Ga/ 177 Lu-labeled multimer PSMA tracer conjugating with PEG chain, including [ 68 Ga]Ga-DOTA-(1P-PEG 4 ), [ 68 Ga]Ga-DOTA-(2P-PEG 0 ), [ 68 Ga]Ga-DOTA-(2P-PEG 4 ), and [ 68 Ga]Ga/[ 177 Lu]Lu-DOTA-(2P-PEG 4 ) 2 , which showed an advantage of a multivalent effect and PEGylation to achieve higher tumor accumulation and faster kidney clearance. To figure out how structural optimizations based on a PSMA multimer and PEGylation influence the probe's tumor-targeting ability, biodistribution, and metabolism, we examined PSMA molecular probes' affinities to PC-3 PIP (PSMA-highly-expressed PC-3 cell line), and conducted pharmacokinetics analysis, biodistribution detection, small animal PET/CT, and SPECT/CT imaging. The results showed that PEG 4 and PSMA dimer optimizations enhanced the probes' tumor-targeting ability in PC-3 PIP tumor-bearing mice models. Compared with the PSMA monomer, the PEGylated PSMA dimer reduced the elimination half-life in the blood and increased uptake in the tumor, and the biodistribution results were consistent with PET/CT imaging results. [ 68 Ga]Ga-DOTA-(2P-PEG 4 ) 2 exhibited higher tumor-to-organ ratios. When labeled by lutetium-177, relatively high accumulation of DOTA-(2P-PEG 4 ) 2 was still detected in PC-3 PIP tumor-bearing mice models after 48 h, indicating its prolonged tumor retention time. Given the superiority in imaging, simple synthetic processes, and structural stability, DOTA-(2P-PEG 4 ) 2 is expected to be a promising tumor-targeting diagnostic molecular probe in future clinical practice.