The invention provides a MEMS polysilicon nanofilm pressure sensor chip and a manufacturing method thereof, and relates to a sensor chip and a manufacturing method thereof. The sensor includes a monocrystalline silicon substrate (1), a pressure sensing film (4) having the section of a flat polysilicon is arranged on the silicon substrate, an enclosed cavity (2) is formed between the pressure sensing film and the substrate by taking silica as a sacrificial layer, the upper surface of the pressure sensing film (4) is provided with four polysilicon nanofilm force sensing resistors (5), the four polysilicon nanofilm force sensing resistors (5), the pressure sensing film (4), and metal leads are isolated by insulation layers (7), the four force sensing resistors (5) are connected to form a Wheatstone bridge via the metal leads to convert the pressure to voltage to output, and sealed corrosion holes (3) are arranged outside the edge of the pressure sensing film (4). The sensor preparing method is compatible with integrated circuit technology and is easy to integrate. The sensor has the characteristics of high linearity sensitivity, wide operational temperature range, high overload capability, easy integration, and low cost.