Maintaining the quality-of-service (QoS) requirement while eliminating interference is an important but difficult task in the downlink MC-DS-CDMA with two-dimensional (2D) spreading. To achieve this goal, we integrate the power control (FC) mechanism and the interference avoidance code assignment strategy. This joint policy is to firstly eliminate interference via the interference avoidance (IA) code assignment strategy and then maintain the QoS via power control. To facilitate the code assignment strategy, by performance analysis, we define a new PC-based multiple access interference (MAI) coefficient. Thanks to the help of the MAI coefficient, we can evaluate each candidate code by quantitatively predicting the possible interference it may produce. With this interference pre-evaluation, the extra MAI m the system can be avoided. Subsequently, the power control mechanism can maintain the QoS using less power to further eliminate MAI. The simulation results show that the proposed joint scheme can maintain a predefined signal quality and achieve a high code admission rate while reducing the power consumption to 68% in the considered case.