In the Third-Generation Partnership Proposal technical specification, the 3GPP Wideband Code Division Multiple Access standard will support data rates up to 2 Mbps with Orthogonal Variable Spreading Factor (OVSF) codes. The use of OVSF codes can provide variable data rates to flexibly support the applications with various Quality of Service (QoS) classes introduced by Universal Mobile Telecommunications System (UMTS). In tradition, bandwidth congestion rate can only represent the bandwidth occupied ratio, which may not be suitable for OVSF code tree Wide-band Code-Division Multiple Access (W-CDMA) system. In this paper, we propose a new bandwidth adaptation scheme and a novel parameter, Dense Ratio (DR), which efficiently represents a W-CDMA downlink status between data traffic sources. After simulations, our proposed bandwidth adaptation scheme can reduce the new call blocking probability and thus improve the system utilisation for W-CDMA systems.