Abstract: The potential in alternating current field which Kirchhoff ＇s second law said is in fact the Coulomb gauge scalar potential. The concise and practical expressions of Kirchhoff ＇s second law are given,and we expound in lumped element circuit the practical expression how to degenerate into the form known widely. At last the new way of establishing equations of uniform transmission line is given,this method based on the practical expression of Kirchhoff ＇s second law and the law of conservation of charge.

Key words: Kirchhoff ＇s second law, Coulomb gauge, electromagnetic scalar potential, uniform transmission line equations