According to the new requirements that type testing of products must be in accordance with the standards of the importing country, taking harmonic current emission testing of vacuum cleaners as an example, the study analyzed the technical details of the IEC standards about harmonic current emission. The operation conditions of Equipments Under Test(EUT) were discussed. The cause of the firing-angle being set to 90° was explained theoretically. The relationship between the firing-angle and the power output of EUT was identified through experiments. A very useful testing flow was put forward. A kind of vacuum cleaner was used to be tested，and the results demonstrated the validity and accuracy of the conclusion of this paper.