The present invention belongs to the field of pharmaceutical technology, more specifically relates to optically pure benzyl-4-chlorophenyl-C-glucoside derivatives represented by formulae (II) and (III), a process for preparing these compounds and intermediates thereof, a pharmaceutical formulation and a pharmaceutical composition containing these compounds, and the use of the optically pure benzyl-4-chlorophenyl-C-glucoside derivative as a sodium glucose co-transporter (SGLT) inhibitor in manufacture of a medicament for treating and/or preventing diabetes mellitus (including insulin-dependent diabetes mellitus and non-insulin-dependent diabetes mellitus) or diabetes-associated diseases (including insulin resistance disease and obesity) or
