A three-dimensional wind-resistant design method for a power transmission tower includes the steps: carrying out a rigid model balance force measurement wind tunnel test by means of increasing and decreasing components of cross arms, and measuring shape coefficients of a power transmission tower body with the overlong cross arms and all direction wind angles of the cross arms; and obtaining wind load cross-power spectrums, based on a base response force spectrum, of a downwind direction, an across-wind direction and a reversing direction of each node by means of a height sectioning estimation method of power transmission tower node wind load spectrums, and obtaining three-dimensional equivalent node wind load directly used for power transmission tower wind-resistant design by the aid of a load-response correlation method based on the node wind load cross-power spectrums. The three-dimensional wind-resistant design method for the power transmission tower takes the influence of different wind direction angles on the shape coefficients into consideration, truly measures shape coefficient values of the overlong cross arms serving as special components, breaks through normative limitations, and takes full account of characteristics of the power transmission tower with the overlong cross arms, wind induced response of the power transmission tower in the downwind direction is calculated, and simultaneously wind induced response of the power transmission tower in the across-wind direction and the reversing direction is calculated, so that safety, economy and reliability in design of the power transmission tower with the overlong cross arms are guaranteed.