Prostate cancer is the second leading cause of cancer-related death in men. MicroRNAs are thought to have a potential role in tumorigenesis. In this paper, the significance of the expression level of mir-21 in prostate cancer patients and its Meta-analysis were investigated. For this study, MiR-21 and prostate cancer detection methods were first described in detail, and then a model was established for the detection of prostate cancer, and the image was divided into foreground and background parts according to the selected threshold, and the prostate image was detected. The data of prostate cancer patients were collected, divided into four types: well-differentiated cancer, moderately differentiated cancer, poorly differentiated cancer and undifferentiated cancer, and then they were stained to analyse the changes in the expression level of miR-21 in the experimental subjects. The experiments showed that when circulating miR-21 levels were elevated, potential patients were 4.3 times more likely to develop cancer than healthy controls.