In order to reduce the uncertainty of the system, this paper analyzes the sources of the uncertainty of the steady-state pressure measurement system of the test-bed, analyzes the important factors of reducing the uncertainty of the steady-state pressure measurement system, and proposes the corresponding improvement methods. The in-site calibration method of pressure sensor is used to reduce the uncertainty caused by the difference between the measurement system and the calibration system. The cubic spline interpolation method is used to compensate the temperature of the pressure sensor and reduce the uncertainty of the influence of the working environment temperature on the pressure sensor. Through data verification, the two improved methods effectively reduce the uncertainty of the system. The improved method has important popularization and application value in other engine tests and related assembly tests.