1. An apparatus for measuring depth, comprising: an image analysis unit, receiving a plurality of reference blurred images, analyzing a plurality of grey scales of the plurality of reference blurred images, producing corresponding reference grey-scale distribution data, in which the plurality of reference blurred images corresponding to a plurality of reference depths, respectively; and a blur comparison module, producing a blur model according to the reference grey-scale distribution data and the plurality of reference depths; where the image analysis unit receives a target blurred image, analyzes the grey scales of the target blurred image, and produces and transmits target grey-scale distribution data to the blur comparison module; the blur comparison module compares the target grey-scale distribution data according the blur model, and produces depth information corresponding to the target blurred image.