The invention discloses a method for adjusting installation position error of a T-shaped truss, including the following steps: (1) primarily placing the T-shaped truss; (2) accurately measuring installation angular deviations alpha 1, alpha 2, alpha 3 and alpha 4 of a cross truss and a vertical truss in a horizontal direction and a vertical direction respectively, and a vertical distance L from a point E to the vertical truss; (3) calculating a horizontal cycle error delta r of the point E; and (4) checking whether the horizontal cycle error delta r of the point E satisfies installation requirements, adjusting values of the alpha 1, the alpha 2 and the alpha 3, and then returning to the step (2) to continue operations until the delta r satisfies the installation requirements. The method creates a truss position error analyzing model, the adjusting method is simple and effective, and demands on high precision installation of the truss structure in practical projects can be satisfied. The method can be used for precision adjustment for a large truss structure guide rail transportation device which has demands on high precision and can be temporarily installed and detached.