The invention discloses a method and system based on a passive optical network for collecting power grid information and relates to the technical field of power grid information collection. The method comprises the steps that the power consumption information of individual users which is metered by an intelligent electronic meter is collected, and modulating signals are obtained after the collected power consumption information of the individual users is modulated through an orthogonal frequency division multiplexing technology; the modulating signals are transmitted to power grid substations belonging to the individual users through a power-line network, and the received modulating signals are demodulated in the power grid substation; the power consumption information of all the individual users within the jurisdiction of the power grid substation is converted to passive optical network signals and transmitted to a power grid master station through fiber optics. Thus, it can be seen that the power consumption information of the individual users is sent to the power grid substation by relying on the power-line network, and transmitted to the power grid master station through the passive optical network of the power grid substation. The method and system based on the passive optical network for collecting the power grid information have the advantages that the collection treatment of the power grid information can be carried out on the areas which are not achievable in being covered by the optical communications network, thereby increasing the collection range of the power grid information and improving the collection efficiency.