Objective To compare and explore the impact of radical prostatectomy, external beam radiation therapy, and prostate brachytherapy on sexual function of patients with prostate cancer. Methods A total of 80 prostate cancer patients admitted to the Urology Department of Ji'an Central People's Hospital from January 2020 to December 2022 were retrospectively analyzed. According to the treatment plan, they were divided into a surgical resection group (n=26, underwent radical prostatectomy), an external beam irradiation group (n=28, treated with high-energy X-rays or particle beams directed at irradiate tumor cells from outside the body), and a brachytherapy group (n=26, radioactive material placed directly into the prostate to act on cancer cells). General data such as age, body mass index (BMI) and Gleason score were collected for all patients. Patients were assessed for erectile dysfunction using international index of erectile function (IIEF) scale, for sexual desire using sexual dysfunction index (SDI) scale, and for sexual function using male sexual health questionnaire (MSHQ) scale. Six months after the end of treatment, the patients' anxiety and depression were assessed using self-rating anxiety scale (SAS) and self-rating depression scale (SDS). Results There were no statistically significant differences in age, BMI and Gleason score among patients in each group (P>0.05). The brachytherapy group demonstrated a higher rate of no erectile dysfunction compared to surgical resection group and external beam radiation group (P<0.05), and lower rates of mild and moderate to severe erectile dysfunction compared to surgical resection group (P<0.05). The external beam irradiation group showed a higher rate of no erectile dysfunction and lower rates of moderate to severe erectile dysfunction compared to surgical resection group (P<0.05). The brachytherapy group showed higher scores in sexual fantasy, sexual desire, sexual frequency and total SDI score than those in surgical resection group and external beam radiation group (P<0.05). The external beam radiation group also had higher scores in these areas compared to surgical resection group (P<0.05). The total sexual function score was higher in brachytherapy group compared to the other two groups (P<0.05), and the external beam irradiation group had a higher sexual function score than surgical resection group (P<0.05). The SAS and SDS scores in brachytherapy group were lower than those in surgical resection group and external beam radiation group (P<0.05). Conclusion Among the treatment methods for prostate cancer, prostate brachytherapy is relatively more effective in maintaining sexual function, especially in terms of erectile function and sexual desire, outperforming radical prostatectomy and external beam therapy.