The invention discloses a voltage dip duration detection method based on information entropy. The method can be applied to voltage regulation devices such as a dynamic voltage correction device; and in the devices, a control system finishes detection of the voltage dip duration by use of an information entropy algorithm according to the voltage monitoring data acquired in real time. The method comprises the following steps of: calculating the information entropy value of a voltage dip signal; locating the start and stop moments of the voltage dip signal through threshold selection; and performing adaptability analysis on the detection method. The method disclosed by the invention has a simple detection principle, and can accurately judge the start and stop moments of the voltage dip according to the sudden change of the entropy value; when noises exist, the maximum detection error is not greater than 0.6 ms, thus the detection precision is relatively high; the algorithm mainly involves in simple sum operation and addition/subtraction operation, and is easy to realize in projects; the method disclosed by the invention has relatively strong adaptability to the voltage dip caused by the single-phase fault or three-phase fault; and for a dynamic voltage correction device, the invention provides a new method for detecting voltage dip duration.