The invention discloses a method for decreasing the basic error of a pressure sensor. The measuring range of a pressure calibration instrument is equally divided, the pressure sensor generates M pressure measurement data and the corresponding voltage, the measuring range of the pressure sensor is calibrated one by one to obtain M pressure calibration coefficients, the M pressure calibration coefficients are respectively multiplied by X times to obtain the calibration m of pressure calibration values C, the calibration m of the M pressure calibration values C is multiplied by the measurement mof M voltage measurement values V generated by the pressure sensor at the corresponding pre-calibrated air pressure to obtain M pressure values Pm, and the accuracy grades of a group of pressure values Pm are determined and are compared; and when the detected accuracy grades are not increased any more, the optimal value of the coefficients of the measuring range of the sensor is obtained. The invention can decrease the basic error of the pressure sensor and enhances the basic measurement accuracy of the measurement of the pressure sensor.