In view of the shortcomings of the field calibration method of wind speed sensors in service, this paper discusses the improvement of the calibration equipment of cup wind speed sensors widely used by meteorological departments, and uses the startup wind speed calibrator to calibrate the wind speed sensors in low wind speed section, so as to solve the problem that the wind speed calibrator cannot detect the overall performance of wind speed sensors, and realizes the instrument traceability of cup wind speed sensors and reaches the laboratory wind tunnel standards. After calibrating the wind speed sensors with the improved field calibration method, the fitting linear regression equation is compared with the wind tunnel calibration results. It is found that the improved method can basically meet the needs of the field calibration of wind speed sensors.