A method for expanding a high-availability server cluster is disclosed. The method includes configuring at least two nodes comprised in a server cluster to be expanded as one or more server units, each server unit consisting of at least two nodes; configuring a newly added node into the server cluster, and configuring the newly added node as at least one newly added server unit in the server cluster; and broadcasting routing information of the newly added server unit. The method realizes an expansion of a server cluster by adding a newly added server unit to the server cluster, i.e., increasing the number of server units in the server cluster, so that the number of sessions and processing performance of the expanded server cluster can be improved, with a relatively low expansion cost.