The syphilis infection and pathogenesis process is characterized by periodic latency and re-emergence, the cause of which is related to the production of immunity of the organism. When the immunity of the organism decreases, syphilis spirochetes can invade certain parts of the organism and cause a mucosal rash. When syphilis causes a mucosal rash, it should be examined promptly. The tests often done are: 1, pale spirochete examination: is an important method of syphilis etiology diagnosis, as a strong evidence of syphilis laboratory diagnosis. The examination methods are: ① dark field examination; ② smear staining examination; ③ immunofluorescence examination; ④ rabbit infection test (RIT); ⑤ tissue section staining examination. Test results: positive in phase I syphilis lesions; positive in phase II syphilis skin, mucosal lesions or blood, detection rate of 80% to 85%; late syphilis skin, mucosal lesions or blood is mostly negative. 2, syphilis serologic test: also known as syphilis serologic reaction, is the main means of immunological examination of syphilis, for syphilis laboratory diagnosis of important indications of this test or clinical application for routine diagnosis; also suitable for screening tests in a large number of people; or used to observe the efficacy; determine whether recurrence or reinfection; for early diagnosis (such as RPR test); used as a quantitative test to determine the intensity of the patient’s reactin, and to exclude the phenomenon of pre-banding; to identify early or late latent syphilis; to identify fetal syphilis and passive reactinemia; if the cerebrospinal fluid is taken for VDRL test, it also helps in the diagnosis of neurosyphilis.