Embodiments of the present invention discloses a method and a device for allocating a group identifier, which can allocate a non-conflict GID to a non-AP STA in an area covered by multiple BSS networks, so that the problem of GID conflict which is occurred when allocating the GID for the non-AP STA can be reduced. A method provided by the embodiment of the present invention includes: dividing all group identifiers (GIDs) into N parts according to number of the GIDs, and allocating the N parts to N basic service set (BSS) networks, which communicate in a multi user - multiple input multiple output (MU-MIMO) mode, respectively for using, where the N BSS networks have a common area, N is a natural number which is bigger than 1; where an access point (AP) in a BSS network allocates a group identifier, which is selected from the group identifiers allocated to the BSS network according to a preset order, to a non-AP Station (STA) in the BSS network.