The neutral point of transformer accessing direct current（DC）blocking capacitor is an effective measure to restrain DC bias.But accessing the DC blocking capacitor will bring changes to the zero-sequence parameters of the system.At the same time，it is still unknown whether there exists the superimposed effect after widely accessing the DC blocking capacitor.A ring-shaped system equivalent model based on the 220kV transformer is developed for calculation and simulation，while making quantitative calculation with the computer-aided coordination for relay in the whole power system in different kinds of circumstances and fault types.The research results show that accessing the DC blocking capacitor has little effect on the line zero-sequence current and voltage，but exerts the greatest effect on the zero-sequence current of transformer neutral point in the accessing substation.The superimposed effect does exist when widely accessing the DC blocking capacitor in the neutral point of transformers.But the effect of the zero-sequence protection is basically negligible after the superposition.