The invention relates to the technical field of optical fiber grating sensing monitoring, and provides a crane structure health online monitoring system in a service center mode. The monitoring systemcomprises a service center which is composed of a central server and a service function assembly, a monitoring system client which is composed of a plurality of fiber bragg grating sensors, a fiber bragg grating sensing demodulator, an optical fiber junction box, an on-site computer and a client-side server, and a matched software system, wherein a plurality of optical fiber branching devices arearranged in the optical fiber junction box, and the plurality of optical fiber grating sensors are distributed on measuring points of the crane. According to the system, the structure health condition of the crane in operation can be monitored on line in real time, safe operation of the crane is guaranteed, structure safety assessment is completed by combining a pre-warning mechanism, quantitative data and safety guarantee are provided for use, maintenance and lightweight design of the crane, and the energy-saving performance and the economical efficiency of the crane are improved.