A method for fabricating a semiconductor structure is provided. The method includes providing a semiconductor substrate; and forming a plurality of semiconductor devices on the semiconductor substrate. The method also includes forming a dielectric layer covering the plurality of the semiconductor devices on the semiconductor substrate; and forming an optical auxiliary layer configured to reflect a portion of a levelness-detecting light and absorb a portion of the levelness detecting light transmitting through the optical auxiliary layer during a levelness-detecting process over the dielectric layer. Further, the method includes forming a photoresist layer over the optical auxiliary layer; and detecting a levelness of the semiconductor substrate and exposing the photoresist layer to form a patterned photoresist layer.