Cognitive Radio can achieve dynamic spectrum access by spectrum sensing. The paper proposes a new scheme to share spectrum employing OFDMA-based Cognitive Radio. To show efficiency and fairness, the paper builds an Asymmetric-Nash-Bargain-Solution- Based utility function and implement a new spectrum sharing algorithm based on sensing contribution weighted proportional fairness through two-user bargaining. The simulation results show that the proposed approach is not only to achieve a fair and efficient allocation of spectrum resources but also to help maximizing the spectrum sensing.