Abstract: A power transmission line dip measurement method is disclosed. The dip measurement method includes installing a measurement instrument at a place where power line support points of steel towers can be seen from the ground, collimating the measurement instrument at the power line support point of one of the steel towers, transmitting a collimated value to a PDA in a wired or wireless manner, collimating the measurement instrument at the power line support point of the other steel tower, transmitting a collimated value to the PDA, calculating the collimated values to display a horizontal angle position of a dip base line, and adjusting an angle of the measurement instrument based on the horizontal angle displayed on a screen of the PDA by a worker, collimating the measurement instrument at a power line dip point as a dip base point, and displaying a dip value on the screen of the PDA.