An apparatus and method for Connection Admission Control (CAC) in a Broadband Wireless Access (BWA) system are provided. In the method, a QoS class of a call requesting connection admission is detected and an application layer required bandwidth is determined using the QoS parameters of a service flow of the detected QoS class. A required bandwidth weight of the QoS class is determined in consideration of a packet header overhead. Per-slot available bandwidths of a reference QoS class and the QoS class are determined using the determined application layer required bandwidth, and a required bandwidth conversion ratio of a corresponding QoS class is determined using the determined per-slot available bandwidths. An equivalent MAC layer required bandwidth is determined using the determined application layer required bandwidth, the required bandwidth weight, and the required bandwidth conversion ratio.