This paper comprehensively reviews the advances and problems in the study of global Ordovician chronostratigrapy for recent years. The discussion is centre on the scope for each series, including the revised Arenig , Llanvirn -Llandeilo , Caradoc and Ashgill , within a global unified Ordovician chronostratigraphic scale,and the biohorizon or zonal level,which is probably selected as a mark for the subdivision of each series and stage boundary. The problems are indicated regarding the study of Ordovician chronasttatigraphy in China at present. A dual ordovician chronostratigraphic scheme both for China and the world is present on the basis of the principal and trend of global Ordovican chronostrastratigraphic subdivision and related data acctunulated by many Chinese geolvgists over a decade or more.