A capacitive pressure sensor with a new movable electric plate structure is presented to improve the output nonlinearity of a MEMS-based capacitive pressure sensor. The movable plate of the sensor is a rectangular memrance made of LPCVD silicon nitride film,and a circular island is added from the center to the edge of the membrane by depositing and patterning a layer of PECVD silicon dioxide. With this structure,the deformation of the movable plate of the capacitive pressure sensor will tend to flat when applying a load of pressure,so that the nonlinearity of stray capacitance near the edge of the entire structure is decreased and the output properties of the sensor is improved. Moreover,the Finite Element Model( FEM) in ANSYS is used to analyze the new structure of the movable electrical plate with different dimensions to obtain the relationship between deflection and pressure and the corresponding stress distribution and a curve fitting based on the least-square method is applied to calculate the output linearity of the sensor. Comparison of the MEMS-based capacitive pressure sensor with a general structure sensor,the output linearity of the proposed sensor has been improved by 48.38%,reaching 1.6%.