A two-dimensional model was established for the first time by coupling moving wire and arc in CMT-WAAM and GMAW-WAAM process, revealing the temperature, potential and droplet transition behavior of droplet metal. The droplet transition and the change of droplet transfer mode under different wire feeding speed were analyzed. The experiments and numerical simulation research found that droplet transition mode is projected transfer in GMAW-WAAM process under 150 A current, with a complete transition period is 14 ms. The droplet transition shows a short-circuit transition mode in CMT-WAAM process, with wire feeding speed of 5.5 m/min and a complete trans-ition period is 20 ms. The droplet transition shows a mixture of droplet transfer and short-circuit transition mode in CMT-WAAM process, with wire feeding speed of 5.5 m/min and a complete transition period is 23 ms. Based on the theoretical research and experimental studies, the mechanism of droplet transfer mode in WAAM was studied, which can provide reference for optimizing parameters.