The invention provides a fabrication method of an MEMS (Micro Electro Mechanical Systems) double layer suspended micro structure, which can fabricate a double layer suspended micro structure. An infrared detector is manufactured by using the double layer suspended micro structure (a suspended micro structure including a first dielectric layer and a second dielectric layer), wherein since the second dielectric layer does not need to fabricate a cantilever beam, thus the second dielectric layer can be made to be larger than the first dielectric layer, so that the infrared detector can have a larger suspension absorption region than an infrared detector of a single layer suspended micro structure, and have a higher infrared response rate. Moreover, the invention further discloses an MEMS infrared detector.