The present invention provides a dual grating sensor having at least two double-sided grating structures for detecting the properties of an analyte. The dual grating sensor includes a substrate, a waveguide layer which is formed on the substrate and has at least two double-sided grating structures, and an upper cover configured on the waveguide layer, wherein a channel is formed between the upper cover and the waveguide layer for the analyte to flow therethrough. A light couples into the waveguide layer via the first double-sided grating structure, transmits in the waveguide layer, and couples out of the waveguide layer via the second double-sided grating structure, such that the properties of the analyte can be detected according to the change of the light intensities of the emergent light. The sensitivity of the dual grating sensor has an additive effect when the light passes through the first double-sided grating structure and the second double-sided grating structure.