A lifetime evaluating system includes a digitalizing unit, an acquiring unit and a determining unit. The digitalizing unit digitizes an original metallographic image of a mechanical element to form a digital image. The acquiring unit acquires a plurality of labels from the digital image. Here, each of the plurality of labels is a set of pixels with a predetermined property. The determining unit classifies the plurality of labels into a class of voids and a class of non-voids based on evaluation data. A lifetime of the mechanical element is determined based on a number of labels in the void class and a size of each of the labels in the void class.