The economical span of UHVAC double-circuit transmission line has great significance to the optimization of tower design and the reduction of project total investment. The economical span of UHVAC double-circuit transmission line is calculated under ideal conditions. Furthermore, its sensitivity is analyzed from climate, terrain, conductor type, ground clearance and tower material et al. The tendency of economical span under various boundary conditions is discussed. The results may provide references for subsequent design of UHVAC double-circuit transmission line.