Abstract: The threedegree-of-freedom(3DOF)galloping equation of a single conductor was derived. 3DOF galloping equation includes three motions: in-plane, out-of-plane and twist motion, so it can completely describe the character of galloping. Based on the stability of differential equation, a concept of critical wind was introduced to estimate the stability of galloping. In addition, a stiffness evaluation approach was introduced to solve the bundle conductor galloping. Consequently, the 3DOF galloping equation can describe not only a single conductor, but also a bundle conductor.