The invention discloses an MEMS pressure sensor and a manufacturing method thereof. The MEMS pressure sensor comprises an MEMS pressure sensing chip, wherein the MEMS pressure sensing chip is arranged at a Wheatstone bridge formed on the crystallographic orientation of a monocrystalline silicon film (110) by four polycrystalline silicon resistors, the monocrystalline silicon film comprises a lower silicon wafer, an upper silicon wafer and a purification layer, a cavity body is arranged on the lower silicon wafer, the lower silicon wafer and the upper silicon wafer are bonded together by hot melt silicon-silicon, the surface of the upper silicon wafer is provided with a passivation layer, the polycrystalline silicon resistors are arranged on the upper silicon wafer by a diffusion process, and a conducting wire of a metal film and a press welding block are etched on the upper silicon wafer. The pressure sensor adopting a silicon-silicon bonding structure can be made in a very small size, the number of chips on each silicon wafer can be increased by 50% or more, the silicon-silicon bonding strength is higher, and the air tightness is better. The cost of the sensor is greatly lowered, and the performance is more stable and reliable. The sensor belongs to a pressure sensor with low cost and high performance and has very extensive application.