Cable tester output voltage has the features of high resistance and short time, the traditional calibration methods can not meet the requirements, leading to inaccurate results. To solve these problems, the authors in the process of developed JJF 14572014, select typical cable testers to source internal resistance test, select common voltmeters to response time test. Experiments show that the cable testers internal source impedance of approximately 10 kΩ ~ 2 MΩ, voltmeter response time of approximately (0.5~1.0) s. Through experiments, has reached the conclusions that the standard voltmeters internal resistance should be higher than 1 GΩ and the response time should be less than the output voltage duration of the instrument was been calibrated.