A three dimensional outline information sensing system includes a variable focus image capturing device, and a processing unit. The variable focus image capturing device is configured to continuously capture a plurality of two dimensional images of an object at a plurality of focal lengths. The processing unit is configured to remove out-of-focus parts of the plurality of two dimensional images and keep on-focus parts of the plurality of two dimensional images, and obtain three dimensional outline information of the object by stacking the on-focus parts of the plurality of two dimensional images according to corresponding focal lengths of the plurality of two dimensional images.