Abstract: Primary users’ behavior with priority in cognitive radio system is investigated. Focusing. on handoff delay, a virtual queuing (VQ) model of spectrum handoff is proposed to analyze the effects of traffic characteristics of primary and secondary users. We derive a piecewise approximation of whole cognitive handoff process and obtain the analytical expression of force termination probability and user capacity. Analytical results and simulation confirm the virtual queuing model of spectrum handoff valid. Also delay violation probabilities affected by diverse primary users’ traffic parameters are compared.