A downlink orthogonal variable spreading factor (OVSF) code assignment method is provided. It is determined whether a spreading factor required by a service request is greater than a remaining capacity of assignable spreading factors of a code tree. If not, the code tree is searched from a root until a node of a layer corresponding to the required spreading factor is reached and thus defined as a first node. During the searching, when a searched node is unassigned, the searching continues leftward in a lower layer; and when the searched node is in an assigned state, the searching continues rightward in a same layer of the searched node. It is determined, from the first node, whether any assignable code is available in the layer corresponding to the required spreading factor. If available, an assignable code is assigned to a communication service corresponding to the service request.