The free vibration characteristics of long-span transmission conductors form the fundamental basis for vibration control design, as their natural frequencies and mode shapes directly affect line safety and the selection of vibration suppression devices. In this study, the three-dimensional linear free vibration governing equations were derived through functional integration of the kinetic and potential energies by using Hamilton’s variational principle. Compared with the conventional integral transform method, an improved meshfree discretization strategy is proposed: the shape functions are constructed using the moving least squares (MLS) method, while the boundary conditions are treated with a fully transformed approach, thereby converting the partial differential equations into ordinary differential equations. Subsequently, a corresponding eigenvalue problem is solved to calculate the first few frequencies of the system, and the effect of conductor natural parameters on these frequencies for the transmission conductor is investigated. The results indicate that the natural frequency decreases when the conductor length becomes larger, and the rate of decrease becomes more gradual as the length increases; it decreases with increasing cross-sectional diameter; it decreases linearly with increasing material density; and it increases linearly with increasing elastic modulus. These findings demonstrate that conductor length, cross-sectional diameter, material density, and elastic modulus all have significant effects on the natural frequency. Among them, length and diameter affect the frequency by altering the conductor’s inertia and structural characteristics, whereas density and elastic modulus govern the frequency from the perspectives of inertia and stiffness, respectively.