Abstract: With the wide application of microelectronic devices, various types of sensitive devices have imposed higher requirements on power quality, among which voltage sag has caused the greatest loss to users. Therefore, this paper first analyzes the necessity of applying custom power technology for voltage sag control in distribution network. And then, the working principle, advantages and disadvantages, and application scope of different kinds of custom power equipment are summarized. On this basis, effective suggestions on voltage sag control are provided for users, including the load sensitivity level evaluation, protection device configuration, distribution system design, custom power scheme making and so on. Finally, with a hospital in Shanghai as an example, a custom power application scheme is designed to improve the resistance ability of the user's power distribution system to voltage sag.