1. An abnormal skin area calculating system, comprising: an image capture module, for capturing skin of a human body to generate a skin image; a database, for storing at least one abnormal skin analysis data; a skin analysis module, for analyzing the skin image by using the abnormal skin analysis data to obtain an abnormal skin area graph in the skin image; and a numerical calculation module, for calculating a pixel area of the abnormal skin area graph, and calculating an actual skin area of the human body corresponding to the abnormal skin area graph with an area calibration parameter.