The invention discloses a DNA methylation marker for psoriatic arthritis (PsA), a diagnostic reagent and applications thereof. Including 6 methylation sites: one or more of chr14:38061326, chr14:38061320, chr9:128585454, chr6:37225002, chr3:101901234, chr6:97369501. The present invention uses specific DNA methylation sites as molecular markers for the first time to assist in the screening of psoriatic arthritis and rheumatoid arthritis (Rheumatoid Arthritis, RA) patients, opening up a new way for diagnosis in this field and way. The invention utilizes whole blood of patients to detect DNA methylation sites to achieve the purpose of early diagnosis of PsA, requires less blood samples, is convenient and easy to carry out, and has good application prospects.