Recent interest in high-precision machining for mechanical devices and semiconductor devices has created a compelling need for miniaturization of displacement measuring devices with high performance. Here a new method for displacement measurement based on self-imaging effect in a double-optical-micrograting structure is proposed. Optical field distribution behind an optical micrograting with period of~6.5μm is analyzed theoretically. And transmission properties of the double grating are investigated. Sinusoidal signals are obtained within a range of 1mm experimentally. Using a subdivision process with a multiple factor of 100, displacement measurement with resolution of 64.5nm is demonstrated. Benefitting from acompact structure and a high stability, the method shows great potential in applications such as miniaturized displacement measuring devices and systems.