The early detection of disease especially tumor in its infant stage is extremely important for saving patient life and reducing medical cost. As is well known, an abnormal temperature on skin surface generally implies certain disease state. However, this method is still subjected to certain limitations such as low accuracy and sensitivity. Here, noticing that the human body is sweating all the time which has strong relationship with human health status, we proposed to adopt the sweating state as an effective index for disease diagnostics based on thermal infrared image mapping. Through theoretical evaluation and experimental measurement, it was discovered that, the quantity of sweating from human skin surface due to being covered by a thin film provides a significant signal for health evaluation and affects significantly the real temperature of skin surface. Through intentionally controlling the sweating, the disease can be more easily diagnosed via a far-infrared image equipment. Comparative evaluation on normal or tumor skins indicate that, if controlling sweating by covering skin with a thin film to prevent release of sweat, the temperature rise will differ a lot between these two cases, say about 2.43degC vs. 4.21degC. Therefore, taking account of the quantity of sweating and the final surface temperature abnormality, a better diagnostics on human disease can be expected. This offers a new auxiliary diagnostic modality and extends the working capacity of a conventional infrared thermometer.