The present disclosure provides MEMS devices and their fabrication methods. A first dielectric layer is formed on a substrate including integrated circuits therein. One or more first metal connections and second metal connections are formed in the first dielectric layer and are electrically connected to the integrated circuits. A second dielectric layer is formed on the first dielectric layer. An acceleration sensor is formed in the second dielectric layer to electrically connect to the one or more first metal connections. One or more first metal vias are formed in the second dielectric layer to electrically connect to the second metal connections. A pressure sensor is formed on the second dielectric layer to electrically connect to the first metal vias. The MEMS devices provided by the present disclosure are compact in size through the integration of the acceleration sensor and the pressure sensor.