A micro displacement sensor includes a first photonic crystal module, a second photonic crystal module, a light source and a detector. The first photonic crystal module includes a first substrate and a plurality of first photonic crystals, disposed on the first substrate and are arranged in a matrix. The first photonic crystals define a first light-guide channel having a light input end and a light output end. The second photonic crystal module includes a second substrate, disposed parallel to the first substrate, and a plurality of second photonic crystals, disposed on the second substrate and are arranged in a matrix. The second photonic crystals define a second light-guide channel having a light coupling end and a light detected end. The light source is disposed adjacent to the light input end. The detector is disposed adjacent to the light detected end.