The invention provides a data-updating method in a distributed system. The distributed system at least comprises a first node and a second node, wherein source data are stored in the first node; auxiliary data corresponding to the source data are stored on the second node; and the first node sends an updating operation instruction related to the source data to the second node which locally updates the auxiliary data according to the updating operation instruction so that the auxiliary data are updated to be consistent with the source data. The invention utilizes the characteristics of a movable agent to send the updating operation instruction to a receiving terminal by code migration while not sending data or files; the receiving terminal reconstructs migrated updating instruction codes on site and locally updates the auxiliary data. Accordingly, the data quantity to be transmitted is remarkably reduced.