The present disclosure relates to a method for detecting focal plane based on a grating Talbot effect, the function of which is to detect position of a silicon wafer in a photolithography machine in real time so as to implement an adjustment of leveling and foal plane of the silicon wafer in a high resolution. The detection system utilizes a phase change of “self-image” generated by a grating Talbot effect caused by defocusing of the silicon wafer, so as to accomplish the detecting for focal plane of the silicon wafer in the photolithography machine in a high resolution: if the silicon wafer is at a focal plane, the imaged wavefront by the grating is a planar wavefront; and when the silicon wafer is defocused, the imaged wavefront is a spherical wavefront. Such a detection system has a simple structure, a higher anti-interference capability and a perfect adaption of the process.