The invention relates to the field of power systems, in particular to an online assistant decision making method for large power grid restoration. Corresponding steps of the online assistant decision making method are carried out in different selected working modes, and the working modes include a real-time assistant mode and a research and analysis mode. The online assistant decision making method has the advantages that the merit that dispatchers and equipment operators of a power plant and a transformer substation are familiar with the traditional plan type system restoration scheme when the traditional plan type system restoration scheme is adopted is kept in the real-time assistant mode, the work intensity of plan formulation personnel is relieved, the assistant decision making speediness, accuracy and reliability for power system restoration are embodied, and shortcomings that an actual condition of a power grid which is developed quickly is inconsistent with a designed condition of a plan, restoration paths involved in the plan are infeasible and the like are overcome specifically; almost all computation types which are possibly involved in formulating a common power grid black-start scheme are integrated in the research and analysis mode, typical power grid partition computation for large power grid restoration is added into the research and analysis mode, a scheme draft generating function can be realized, and the expenditure of time spent on integrating different result files is greatly saved.