Aiming at the problem of large measurement errors in input resistance, the physical mechanism and practical reasons were analyzed. Several main factors affecting the uncertainty of input resistance measurement were discussed, including standard voltage, measurement voltage, standard resistance value and error, and so on. The main measures to reduce the uncertainty of input resistance measurement were given, that is, the closer the value of standard resistance and input resistance, the better, and the two should be in the same order of magnitude, moreover, the difference between two different excitation voltages should be as large as possible. The evaluation results of input resistance measurement uncertainty are provided through an example, and both the correctness and feasibility of the process are proved.