A grouping method of user devices comprises configuring one or more codes for each of the user devices by a base station wherein each of said one or more codes corresponds to a delay tolerance, performing a grouping task by the base station according to the delay tolerances and a determining result of channel-usage demand corresponding to each of the user devices so as to form one or more first-type groups and one or more second-type groups wherein each first-type group corresponds to a first-group delay tolerance and each second-type group corresponds to a second-group delay tolerance, and performing a selection from user devices in the first-type groups and the second-type groups to form one or more target groups by the base station according to the first-group delay tolerances and the second-group delay tolerances.