Four sets of mono-element internal-Sn (MEIT) wires which have different Sn-Cu ratio and 1 at% Zr addition in one wire were designed and fabricated for investigating A15 phase formation kinetics of ND3 Sn superconductors. All samples underwent a 210degC/50 h + 340degC/25 h thermal duration for Cu-Sn alloying prior to the A15 phase formation heat treatment (HT). Four reaction temperatures of 650degC, 675degC, 700degC, and 725degC were chosen to study the temperature and time influence. All the heat- treated samples were examined by scanning electronic microscope for A15 layer thicknesses that were then plotted versus HT time at different temperatures and were nonlinearly fitted. Superconducting quantum interference device magnetization measurements were used to determine the inductive JC variations for the heat- treated wires. The obtained results demonstrate that the A15 phase growth is promoted by four factors: reaction temperature elevation, reaction time extension, Sn-Cu ratio enlargement, and the alloyed Zr addition. The phase formation kinetics of MEIT Nb3Sn superconducting wires is in agreement with Yn = K(T)t relation and the A15 growth exponent n is affected by HT temperature and Zr alloying.