Whether syphilis is still contagious after injection depends mainly on whether it is cured or not. If under the guidance of the doctor, the full amount of regular injections of anti-plum treatment and regular review, syphilis has been completely cured, is generally not contagious; but if the syphilis is not cured, it is still contagious. At present, the clinical anti-plum treatment is mainly the use of penicillin treatment, such as benzylpenicillin, procaine penicillin and so on to completely kill the syphilis spirochete; penicillin allergy can be used doxycycline treatment. Adequate and regular use of antibiotics is the key to the treatment of syphilis, and also the key to the complete cure of syphilis. Depending on the course of syphilis, the duration of penicillin or doxycycline application varies, and syphilis can not be cured immediately after injection. For advanced syphilis, if the treatment is not effective, the second course of treatment should be carried out at an interval of 2 weeks. Syphilis symptoms and serologic tests should be monitored regularly after adequate and regular anti-syphilis treatment. Syphilis is not contagious if the clinical symptoms have completely disappeared and the serologic tests are negative on a regular basis for a sustained period of time. Syphilis is mainly transmitted through sexual contact, and to a lesser extent through mother-to-child transmission, blood transfusion or organ transplantation. It is recommended to avoid high-risk sexual behavior and protect yourself from infection.