Prostate-specific antigen (PSA) is produced primarily by prostate epithelial cells and is useful for early diagnosis of prostate cancer, monitoring treatment response and determining prognosis. The vast majority of PSA in serum originates from the prostate gland and is organ-specific, but is not a specific antigen for prostate cancer. Although the normal value of total PSA is generally set at 0-4ng/ml, the normal value of PSA often needs to be adjusted clinically according to the patient’s age. The reference values (Tandcm-R method) are 40-49 years: 0-2.5ng/ml; 50-59 years: 0-3.5ng/ml; 60-69 years: 0-4.5ng/ml; 70-79 years: 0-6.5ng/ml. Serum PSA can also be elevated in the following conditions: prostatitis, urinary retention, rectal examination, prostate trauma, prostate biopsy. Therefore, in the presence of these factors, it is necessary to wait for about 1 week to 2 weeks before performing a PSA review. The ratio of free PSA to total PSA is also incorporated clinically to improve diagnostic accuracy; if it is less than 0.2, it suggests the possibility of malignancy. In addition, continued use of 5α reductase inhibitors for more than 6 months can reduce serum PSA levels back by about 50%, which needs to be doubled when calculating PSA. For patients with significant PSA elevation or abnormal ratios excluding the above factors, an outpatient appointment for prostate puncture is recommended for a definitive diagnosis.