With the advance of the Coal-to-electricity project, the harmonic current is injected into distribution networks from a large number of electric heating radiators, and the voltage sag is simultaneously resulted in, which have an immediate impact on the power quality of the distribution networks. On the basis of physical model analysis and practical load data, the differential analysis is carried out for the harmonic contents of different types of electric heating radiators. The simulation model of the radiators is constructed under different operation conditions. The influence degrees of harmonic contents and voltage sag resulted from the radiators are then analyzed and the corresponding measures are determined. Case study shows that the harmonic contents and the voltage sag in the low voltage distribution networks increase in varying degrees with adding the permeability of the radiators. Therefore, there is a need to adopt corresponding measures including equipment improvement and operation optimization to restrain these power quality problems.