A method for inspecting a grating biochip comprises the steps of irradiating a grating biochip using a light beam, measuring a diffracted light using a photodetector, selecting a plurality of parameters of the grating biochip, and optimizing the parameters to enhance the detection sensitivity, wherein the diffracted light is generated by the light beam passing the grating biochip. The grating biochip comprises a grating structure including a semiconductor substrate, a grating positioned on the semiconductor substrate and a dielectric layer covering the grating and the semiconductor substrate. The sample of the biochip is positioned on the grating structure.