Malignant melanoma tends to metastasize early, and its prognosis is extremely poor and life-threatening in advanced stages. Tumor size and lesion thickness are the most common imaging parameters used to detect melanoma. While changes in mechanical properties during the disease process are closely related to the tumor's basic composition and cellular activity, and are directly linked to its invasiveness and metastatic potential. Here, we present a dual-modality imaging system that combines photoacoustic absorption imaging (PAI) and photoacoustic viscoelasticity imaging (PAVEI) for the staging biopsies of melanoma. The tumor size and thickness can be accurately evaluated by PAI, and PAVEI helps to characterize the tumor viscoelasticity through the phase delay of photoacoustic signals. Experimental results demonstrate that the PAI-PAVEI system can comprehensively characterize the absorption characteristics and mechanical properties of tumor lesions, thereby providing essential reference for the early diagnosis, staging assessment, and efficacy prediction of melanoma.