Due to the fast-growing demand for network capacity in wireless networks, the characterization of network capacity has become one of the most fundamental and pressing issues. While there have been considerable efforts to study CDMA systems at both the physical layer and network layer, the network capacity of power-controlled CDMA systems with linear receivers, especially in fading environments, is not well-understood. In this paper, we study a single cell synchronous CDMA system equipped with the matched filter receiver in fading channels, and identify the network capacity for single-class systems and the network capacity region for multiple-class systems assuming known distributions of received powers of mobile users. Both the network capacity and network capacity region can be uniquely expressed in terms of the users' QoS requirements and the distributions of the received powers. We also find the tightest upper bound of the network capacity over all possible distributions of received powers, and explore the concepts of effective target SIR and effective bandwidth, which play an important role in determining the admissibility and characterizing the network capacity.