This paper proposes a new spectrum handoff approach for multiple channels cognitive radio networks to support delay sensitive applications such as VoIP. The delay probability is estimated to determine whether and how to perform the handoff operation. Moreover, traffic prediction on licensed channels is also required in order to estimate the impairment in the delay. Since, the error of prediction still cannot be solved totally, therefore the backup channel solution is proposed to reduce the harmfulness of this impact. The delay probability density function is through various strategies of spectrum handoff for multiple channels cognitive radio.