The invention relates to an online optimization simulation system for a complex distribution network, comprising a data layer, an encapsulation layer, and a front end. The system is characterized in that the data layer, the encapsulation layer and the front end are connected in sequence; the data layer is used for acquiring online data and local data of a distribution network and initializing the online data and the local data of the distribution network; the encapsulation layer is used for encapsulating simulation calculation functions into simulation services (namely, one simulation calculation function corresponds to one COM component) and automatically matching out an optimal algorithm to solve an objective function minimum model; and the front end is used for providing a unified human-computer interaction unit to call the simulation services of the encapsulation layer. With the system provided by the invention, the online data of a distribution network can be extracted, parsed and cleaned. A service-oriented optimization calculation architecture is designed, and an optimization calculation method based on automatic matching of multiple algorithms is put forward. Global multi-mode and regionally-accurate online continuous optimization simulation of a large-scale complex distribution network is realized, and the operation efficiency and decision analysis level of a complex distribution network are improved.