A method, device and system for managing resources in networks are provided, which relate to the field of data communication. The method includes the following steps. A resource manager (RM) sends a first request message according to a received resource request message, to request an access node (AN) to perform admission control. After receiving an admission control result indicating whether a resource requested by the resource request message is admitted, the RM sends a response message of the resource request message. Therefore, when multicast/unicast connection admission control (CAC) that supports shared bandwidth is realized, flow fusions of user line configuration between the AN and a broadband remote access system (BRAS, and policy distribution between a resource and admission control subsystem (RACS) and the BRAS are guaranteed; and sharing of bandwidth resources is realized to avoid waste of the bandwidth resources.