The disclosed invention is a MEMS environmental sensor and preparation method thereof. A transfer cavity is produced in the middle of a transfer substrate of a MEMS environmental sensor, and a transfer medium is located inside the transfer cavity. The surface area of an input port is larger than the surface area of an output port. An elastic transfer membrane is provided on the surface of the input port, and an elastic pressure membrane is provided on the surface of the output port. A load bearing cavity is provided in a load bearing substrate, a magnetic sensing element is positioned inside the load bearing cavity, and the load bearing cavity partially overlaps with the output port. The surface area of the input port of the transfer cavity is larger than the surface area of the output port, and on the basis of Pascal's principle, differences in the volume of the transmission cavity are used to transform a small displacement in a region of large volume into a large displacement in a region of small volume. In addition, because the output port and the end of the output port at least partially overlap, and a magnetic sensing element is arranged in the load bearing cavity, a change in displacement is produced, producing a change in a magnetic field, that is converted into a change in electrical resistance, which provides high-sensitivity and low-power detection.