A 68-year-old male patient developed multiple painless soybean-sized erythema and papules on the back of the right wrist, and spread to the upper arm without obvious inducement for more than 1 year. Pyoderma gangrenosum was diagnosed at another hospital and immunosuppressive treatment was applied. Erythema and pain in the right upper extremity aggravated with ulceration 3 months ago. Histopathological detection of the lesion in a hospital suggested consistence with chronic granulomatous inflammation, and metagenomic next-generation sequencing (mNGS) of the lesion tissue indicated Mycobacterium marinum. Therefore, the patient was diagnosed as Mycobacterium marinum infection. This article reports the case with Mycobacterium marinum infection, aiming to improve the clinical understanding on Mycobacterium marinum infection, achieve early diagnosis and treatment, and improve patient prognosis.