There is no need to inject penicillin again after the syphilis has turned negative. Syphilis is generally considered to have been cured after the syphilis has turned negative, but it needs to be continuously observed for more than 2 years. Syphilis is a contagious disease caused by syphilis spirochete infection, the body infected with syphilis, the use of penicillin according to the course of standardized treatment, syphilis can be cured. Syphilis antibodies are negative, indicating that the organism has been cleared of syphilis spirochetes, but there is still a possibility of recurrence, and syphilis antibodies should be rechecked regularly. Through the test of syphilis antibody, if it continues to be negative and the general clinical symptoms disappear, it can be regarded as cured, and need to be observed for 2 years. If syphilis recurs, it can still be cured again by penicillin. After the syphilis becomes negative, it is necessary to review the test regularly under the guidance of the doctor.