The self-induction electromotive force of“three-dimensional conductor”in the light of magnetic vector potential is analyzed. The solution of the self-inductance of“three dimensional conductor”unlimited length coaxial cable is given by using the formula The self-induction electromotive force of“three-dimensional conductor”in the light of magnetic vector potential is analyzed. The solution of the self-inductance of“three dimensional conductor”unlimited length coaxial cable is given by using the formula E = L| ∂l/∂t|　，then the cause of formation of the self -conductance is discussed visually.，then the cause of formation of the self -conductance is discussed visually.