For an actual large-scale complex grid， rational protection zone division based on wide area relaying engineering applications with centralized structure is one of the key technologies to be tackled. Based on the concept of limitedness of wide area relaying， the principles of protection zone division are discussed， including the selection of the main station， the limited scope of wide area protection， and the basic principles of border region interaction. Each of the lines should be capable of realizing back-up protection in at least one divided area while the number of protected zones in the wide area network should reach the minimum. The graph theory is employed to realize wide area protection system partition and the search method based on 4-level adjacent matrix is proposed， which is simple in principle， convenient to operate， and easy to implement. The simulation results concerning an IEEE 10-machine 39-bus system show the feasibility of this method.