The invention discloses a cross cantilever beam single-column self-balance foundation of a power transmission line and a construction method thereof. The cross cantilever beam single-column self-balance foundation of the power transmission line is located under a power transmission tower leg (7) and is characterized in that cross cantilever beams (1) are arranged at the upper end of a foundation main column (2), and the upper surface of the foundation main column (2) is round; the outer edges of each cross cantilever beam (1) and the foundation main column (2) are provided with guardrails (6)correspondingly; tapered columns (4) are arranged on the cross cantilever beams (1): the foundation main column (2) is vertically arranged, and the lower end of the foundation main column (2) extends to be underground and is cast together with an expansion head (3) through concrete; and a ladder (5) is arranged on the lateral surface of the foundation main column (2) from the ground to the top end of the foundation main column (2). The cross cantilever beam single-column self-balance foundation of the power transmission line overcomes the defects that a foundation in the prior art is small in diameter, small in construction space and high in construction risk, and has the advantage of effectively preventing tower materials from being corroded or submersed.