Based on the actual overhead line fault recorded data of a transmission line in the 220 kV electric power system of Shanxi Province， the current and voltage characteristics at the site of the protection equipment for double-circuit transmission lines on the same pole are analyzed. The action-behaviors of four conventional microcomputer-based line protections with different types and from different manufactures are studied. The problems related to the protection selection of double-circuit transmission lines are highlighted. The results show that:（1） the zero-sequence current but not the voltage can be detected by the protections located at both sides of transmission lines during overhead line fault between different phases;（2） the differential directional elements can be identified accurately;（3） the steady-state phase selection elements formed by the zero-sequence current I0and negative-sequence current I2Acan be used to select phase exactly;（4） the action-behaviors of the zero-sequence directional element is uncertain;（5） both the increase of the measured impedance between phases and the decrease of the measured grounding impedance can not reflect the fault location correctly.