Abstract: To obtain effective signals of droplet, which has become a pressing problem, is essential for droplet transfer control in MIG welding. This paper has introduced the method to detect droplet transfer by means of arc including the experiment sets, testing principle and data processing procedure. It has been discovered that arc spectrum signal can detect and measure the transfer procedure, the transfer modes and the transfer parameters. The arc spectrum signal enjoys excellent quality with high signal amplitude, each transfer mode has its specific signal mode, and the pulse outline corresponds to the development of a droplet transfer procedure. All these features of arc spectrum signal can be easily applied in transfer procedure control, transfer mode identification and stabilization and transfer parameters measurement.