The wire melting phenomenon in alternating current gas metal arc welding (AC-GMAW) process should be carefully observed and analyzed since it is one of the most important representative characteristics of GMAW process. In this study, a new form of wire melting rate equation for AC-GMAW process is proposed based on energy conservation theory and arc physics. Using experimental data, the wire melting rate coefficients of AC-GMAW are obtained through nonlinear regression analysis. The wire melting rate is influenced not only by the current waveform, electrode polarity, and droplet size but also by the shape of the wire tip. That is, if the wire tip becomes more slender, arc heating has more influence on the wire melting. Using the wire melting rate proposed in this research, the uncertainty of calculating wire melting rate coefficients of AC-GMAW can be excluded comparing to existing method.