Based on a rigorous method called the master-slave-splitting method， an AC/DC hybrid state estimator is implemented with minor modification on the state estimation software available for a purely AC system and put into trial operation on the spot in China Southern Grid（CSG）. Specific implementation issues are discussed and treated， including the software's main framework， DC system parameter identification， DC system observability analysis and DC system measurements conversion. Field application experience and effects of the state estimator developed for both the CSG core model and complete model are reported， especially the detailed results of 24-hour continuous operation of the estimator concerning the CSG complete model， to show the accuracy， efficiency， convergence and reliability of 24-hour sustained operation.