The present invention discloses a test method for image sharpness, which can instantly determine the sharpness of a captured image, wherein a captured image is firstly divided into multiple blocks with each block composed of multiple pixels; in each block of the captured image, the pixels having higher sharpnesses are selected, and the sharpnesses of those pixels are summed up to be the sharpness of the related block; the estimated sharpness of the captured image is also obtained similarly; and the estimated sharpness is compared with a threshold value to determine whether the captured image is sharp enough. Thereby, the present invention can test the sharpness of an image fast and correctly and inform the user of the status of the captured image and provide the user with corresponding suggestions.