The present invention relates to network communication field. A method for admission control, an apparatus and a communication system thereof are disclosed according to the present invention. The method includes measuring, by an egress node, traffic from an ingress node, and calculating a current congestion degree; comparing, by the egress node, the current calculated CLE with a last calculated CLE, and sending the current calculated CLE to an admission control decision entity by the egress node if the current calculated CLE crosses a predetermined threshold; receiving and storing the CLE by the admission control decision entity; and making a decision by the admission control decision entity based on the stored CLE, when a service traffic request arrives at the admission control decision entity, and determining whether to admit the service traffic request. According to the method for admission control provided by the present invention in which CLE is transferred proactively, the number of messages for transferring CLE is reduced when calling rate is high, and admission decision procedure is accelerated.