Preparation of high-quality noble nanostructure substrate is vital for the application of surface-enhanced Raman scattering (SERS) technology in ultrasensitive bioassay. In our work, based on the improved Langmuir-Blodgett method, the gold nanorods were extracted from colloid to the interface between the colloid and toluene with the help of ethanol, and fixed by polymethyl methacrylate (PMMA), then a uniform and dense array of two-dimensional domain-like nanostructure was formed in a large area. Next, the plasma clean technology was used to treat the fabricated substrate for enhancing its SERS performance due to the exposed surface of the Au NRs. The experimental results showed that the Au NRs/PMMA substrate exhibited the excellent SERS characteristic and its enhancement factor (EF) achieved 5.49×106 under irradiating of 785 nm laser. In addition, the highly sensitive label-free quantitative detection of tumor maker, prostate specific antigen (PSA), was developed by using Au NRs/PMMA substrate. In the experiments of label-free detection, the Raman characteristic peaks of the PSA were first acquired by comparing the SERS spectra of the PSA standard solution and new-born battle serum solution, and they were mainly located at 823, 1 080, 1 385, 1 586 and 1 640 cm-1. Following, the SERS spectra of PSA standard solution, clinical male serum samples and female serum samples were measured and analyzed to screen the Raman characteristic peaks of PSA associated only with serum PSA levels, and they were located at 649, 680 and 1 640 cm-1. Furthermore, the SERS spectra of α-fetoprotein (AFP) belonging to the glycoprotein same with PSA and human kallikrein 2 (hK2) homologous with PSA were separately measured as two controls, and the extremely specific Raman characteristic peaks of PSA located at 1640 cm-1 were determined and applied in the detection of clinic serum samples. Subsequently, the does-repose curve was obtained by the relationship of the intensities of the Raman peaks at 1640 cm-1 and the PSA concentrations in the standard solutions. Lastly, the PSA concentrations in the clinical serum samples were detected based on the SERS-based label-free detect proposal. It demonstrated that SERS-based label-free detection not only exhibits a well consistency of test data when compared with that of the chemiluminescent immunoassay (CLIA), but also higher sensitivity, and its limit of detection as low as 0.06 ng·mL-1 in the range of 0.1 mg·mL-1～0.1 ng·mL-1. Therefore, it reveals that the proposed protocol has a significant application potential for the quantitative detection of tumor marker.