Abstract: The present invention relates to a calibration method for step attenuator that is utilized in wide-band RF instruments, wherein the step attenuator comprises a plurality of single-stage attenuators connected in series. Use of the method disclosed in this invention allows one to obtain attenuation of the attenuator under various circumstances by computing measurements of single-stage attenuation. As opposed to the conventional calibration method, this invention is advantageous in reducing time for taking measurements, in elevating total attenuation of the object to be tested, and in simplifying the method of calibration and testing.