An integrated MEMS device and its manufacturing method are provided. In the manufacturing method, the sacrificial layer is used to integrate the MEMS wafer and the circuit wafer. The advantage of the present invention comprises preventing films on the circuit wafer from being damaged during process. By the manufacturing method, a mechanically and thermally stable structure material, for example: monocrystalline silicon and polysilicon, can be used. The integrated MEMS device manufactured can also possess the merit of planar top-surface topography with high fill factor. The manufacturing method is especially suitable for manufacturing MEMS array device.