The differences between the power quality at the AC and DC sides, caused by AC-DC converters with constant DC voltage control, commonly exist in low-voltage direct current (LVDC) systems. The voltage deviation isolation(VDI) is one of the typical phenomenons. A method is proposed to analyze the VDI performance and applied in two-stage high-frequency isolated AC-DC converters, which can isolate not only the faults but also the voltage deviation at the AC side and improve the voltage quality at the DC side. First, the voltage deviation isolation ratio(VDIR) is defined to assess VDI. Based on VDIR, the operation characteristics of AC-DC converters with constant DC voltage control are analyzed and the range of VDI is defined. Second, with considering the conditions for stable operation of AC-DC converters, constraints on power transmission limit and static stability limit are used to determine the range of VDI. Third, a simulation model is established and the feasibility and validity of the method are verified. Finally, the main factors affecting the range of VDI are analyzed. Actually, the method proposed is adapted to various types of AC-DC converters with constant DC voltage control.