Abstract: How to improve the efficiency of radio resources which attracts a lot of interest becomes a hot spot problem. The cognitive radio (CR) technology is a new method for solving this problem. And the Non-Contiguous Orthogonal Frequency Division Multiplexing (NC-OFDM) technology provides a good platform for CR systems because of its agile choice mechanism of frequency. This paper introduces a novel adaptive dynamic resource allocation scheme for NC-OFDM based CR system. In this scheme, the secondary users choose their subcarriers and powers to achieve their QoS requirements based on the knowledge of channel detections and proportional fairness principle. The maximal channel capability is achieved accordingly. Meanwhile a decline parameter and terminal types are also introduced during the subccarriers and power allocation, so the interference to the primary users is avoided. The simulation results show that the channel capacity of this algorithm has been improved significantly compared with FDMA and bit error rate compared to same bit allocation algorithm has also been significantly reduced in frequency selective fading channels.