Abstract: In order to explore the cold metal transfer mechanism of aluminum alloy, the droplet transition process was analyzed, and a droplet transfer model was constructed using Mast language. The instantaneous wire feed speed was measured, and the change curve of wire feed speed in CMT transition period was given. Combined with the circuit structure of the arc welding power supply, a simulation platform for the main circuit and control circuit of the CMT welding source was established using Saber software. Through this platform, the simulation of non-united welding with changing boost duration time was carried out. The simulation of electrical signal was compared with the measurement, and the parameter errors of current, voltage, transition frequency ,droplet volume and wire feed speed were discussed. The results showed that the errors between the simulation and the measurement are also less than 10%, which confirmed the accuracy of the CMT simulation platform. It lays a preliminary foundation for understanding the physical process of CMT and optimizing the process parameters.