A three-dimensional printing system, comprising: a light source unit (110, 110'), configured to illuminate an object to be measured and providing the object to be measured with an illumination light (L, L'), wherein the object to be measured is opaque relatively to the illumination light (L, L'); at least one image-capturing module, comprising: an image-capturing unit (122, 122A, 122B, 222), disposed at a side of the object to be measured; and a focus-adjusting lens group (124, 124A, 124B, 224), disposed between the image-capturing unit (122, 122A, 122B, 222) and the object to be measured; the system being characterized in comprising: a processing unit, controlling the focus-adjusting lens group (124, 124A, 124B, 224) to change shooting focal lengths (f) and controlling the image-capturing unit (122, 122A, 122B, 222) to capture a plurality of images of the object to be measured under the different shooting focal lengths (f), wherein each of the plural images comprises a focused local image and an unfocused local image therein, wherein the focused local images are images of overlapped portions of the object to be measured and focus planes under the different shooting focal lengths (f) and the processing unit calculates out a three-dimensional profile data comprising information of a surface profile of the object to be measured according to the focused local images in the images and the shooting focal lengths (f) corresponding to the focused local images; and a printing device, printing a plurality of cross-sectional profiles corresponding to the information of the surface profile of the object to be measured layer by layer. a light source unit (110, 110'), configured to illuminate an object to be measured and providing the object to be measured with an illumination light (L, L'), wherein the object to be measured is opaque relatively to the illumination light (L, L'); at least one image-capturing module, comprising: an image-capturing unit (122, 122A, 122B, 222), disposed at a side of the object to be measured; and a focus-adjusting lens group (124, 124A, 124B, 224), disposed between the image-capturing unit (122, 122A, 122B, 222) and the object to be measured; the system being characterized in comprising: a processing unit, controlling the focus-adjusting lens group (124, 124A, 124B, 224) to change shooting focal lengths (f) and controlling the image-capturing unit (122, 122A, 122B, 222) to capture a plurality of images of the object to be measured under the different shooting focal lengths (f), wherein each of the plural images comprises a focused local image and an unfocused local image therein, wherein the focused local images are images of overlapped portions of the object to be measured and focus planes under the different shooting focal lengths (f) and the processing unit calculates out a three-dimensional profile data comprising information of a surface profile of the object to be measured according to the focused local images in the images and the shooting focal lengths (f) corresponding to the focused local images; and a printing device, printing a plurality of cross-sectional profiles corresponding to the information of the surface profile of the object to be measured layer by layer. an image-capturing unit (122, 122A, 122B, 222), disposed at a side of the object to be measured; and a focus-adjusting lens group (124, 124A, 124B, 224), disposed between the image-capturing unit (122, 122A, 122B, 222) and the object to be measured; the system being characterized in comprising: a processing unit, controlling the focus-adjusting lens group (124, 124A, 124B, 224) to change shooting focal lengths (f) and controlling the image-capturing unit (122, 122A, 122B, 222) to capture a plurality of images of the object to be measured under the different shooting focal lengths (f), wherein each of the plural images comprises a focused local image and an unfocused local image therein, wherein the focused local images are images of overlapped portions of the object to be measured and focus planes under the different shooting focal lengths (f) and the processing unit calculates out a three-dimensional profile data comprising information of a surface profile of the object to be measured according to the focused local images in the images and the shooting focal lengths (f) corresponding to the focused local images; and a printing device, printing a plurality of cross-sectional profiles corresponding to the information of the surface profile of the object to be measured layer by layer. a processing unit, controlling the focus-adjusting lens group (124, 124A, 124B, 224) to change shooting focal lengths (f) and controlling the image-capturing unit (122, 122A, 122B, 222) to capture a plurality of images of the object to be measured under the different shooting focal lengths (f), wherein each of the plural images comprises a focused local image and an unfocused local image therein, wherein the focused local images are images of overlapped portions of the object to be measured and focus planes under the different shooting focal lengths (f) and the processing unit calculates out a three-dimensional profile data comprising information of a surface profile of the object to be measured according to the focused local images in the images and the shooting focal lengths (f) corresponding to the focused local images; and a printing device, printing a plurality of cross-sectional profiles corresponding to the information of the surface profile of the object to be measured layer by layer.