The fault in four-circuit transmission lines is complex, and fault phase detection algorithm of single circuit line can not be used for cross line faults. Aiming at this problem, a method for fault phase selection of four-circuit transmission lines on the same tower is presented based on double-differential phasors of fault currents. Four-summing and double-differential phasors of fault currents can be calculated using a certain transformation matrix for line-line parameter decoupling of four circuit lines. According to fault boundary conditions, the amplitude and phase of three double-differential phasors of fault currents are studied under conditions of different types of faults. Based on this, a novel methodology for fault phase detection for four-circuit transmission lines on the same tower is put forward, which can pick out the fault phases no matter the fault occurs in single line or cross double lines. Simulation results validate that the methodology is correct and reliable under different conditions of load currents, transient resistances, fault point locations and fault types.