Through the experiences of the research on the sites of ancient London citadel (England) from Roman Empire, the author presents his opinions about research approaches in investigation, excavation, research and preservation of Thang Long Imperial Citadel and gives the following proposals: - It is necessary to do an overall planning, defining crucial areas that need surveys, excavation and compulsory and urgent preservation to prevent vandalism. - It is necessary to increase approaches of natural sciences such as geo-physic, remote sensing, and modern graphic measurements to do a survey, discover relics and build adistributive map. - It is necessary to invest in a lot of machinery, equipment and financial supports for the tasks of urban archaeology.