Abstract: An useful protection module of three-phase power was introduced in this paper. The module can detect each power faults such as phase lines opened, voltage of three-phase unbalanced, phase line reversed, etc. The module was completed fully by electronic components. And it’s working function was reliable and the price was lower. It can work as a protecting module of three-phase asynchronous motor or a control set of relay-contactors. So it has a high value in practice.