The negative sequence and the zero sequence component cause three-phase unbalance. IEC proposes to measure the imbalance with the ratio between negative sequence and positive sequence component, ignoring the zero sequence component. Because of the difficulty in obtaining the sequence component, the RMS value of the measured voltage and current is often measured in the project. In contrast, such metrics exist in many forms and do not correspond to the order component metrics. It is urgent to construct a unified unbalance measurement method to considering the zero sequence and the non-correspondence between the quantity measurement and the sequence component. Three-phase unbalance control mainly relies on capacitive compensation, power electronic converter type compensation and commutation. Among them, capacitive compensation can achieve continuous adjustment but can not reduce line loss. Commutation can only be discretely switched and cannot be continuously adjusted. In the future, these two methods should be combined to manage the three-phase unbalance, in order to optimize the compensation effect.