1. An optimization method for a navigation device comprising: recording a plurality of coordinate variation data of the navigation device; analyzing the plurality of coordinate variation data by a data mining technique to generate an analysis result, wherein the data mining technique is an association rule or a clustering rule; generating at least one behavior rule according to the analysis result; and adjusting, by a navigation processor, a route planning result of the navigation device according to the at least one behavior rule; wherein the route planning result indicates a route to a destination not yet reached by a user of the navigation device.