A stress measuring device and a stress measuring method for measuring a stress distribution of an object are provided. The stress measuring method includes: receiving a first-dimension image of the object; marking an area of the first-dimension image to generate a marked area; calculating a first stress applied to the marked area and transforming the marked area to a strained marked area corresponding to a second-dimension image to generate a determination result; and calculating the stress distribution corresponding to the first-dimension image of the object according to the determination result.