The invention discloses a construction method for erecting an electric transmission line double-leg angle steel tower by a helicopter unit, and relates to the field of electric transmission line irontower construction. When a helicopter unit is used for erecting the double-leg angle steel tower, due to the fact that between-section cross-shaped connecting plates are installed on tower sections, difference exists between the root distance sizes of the lifting tower sections and the in-position tower sections, and being in-position is difficult. The construction method comprises the following steps that (1) the between-section cross-shaped connecting plates and main material cross-shaped connecting plates are installed on the lifting tower sections; (2) inner angle wrapping steel and outerangle wrapping steel of the in-position tower sections are connected with and fixed to inner main materials and outer main materials correspondingly, and then abutting auxiliary sleeve pieces are installed on the inner angle wrapping steel and the inner main materials correspondingly; (3) a helicopter hovers and operates to guide the tower sections to be in position through the abutting auxiliarysleeve pieces of the tower sections; after the tower sections are in position, high-altitude personnel installs a small quantity of bolts on two sides of abutting points of the tower sections, and thehelicopter unhooks and leaves; and (5) remaining bolts are installed in a supplementary mode, and the abutting auxiliary sleeve pieces are detached. According to the construction method for erectingthe electric transmission line double-leg angle steel tower by the helicopter unit, the problem of difficult position taking caused by significant difference of the root distance sizes of the liftingtower sections and the in-position tower sections is solved.