UHV（ultra-high voltage） transmission line usually is of longer distance and distinct characteristics of distributed parameters， which may impose problems to the conventional distance relay. This paper analyzes the relationship between the measuring impedance and fault distance of a transmission line with or without shunt reactor. Results of theoretical analysis and simulation indicate that the measuring impedance still has the direct ratio relationship with fault distance when the UHV line has shunt reactors. Hence， the theoretical foundation of conventional distance relay is applicable for the UHV line.