To ensure the optimal use of spectrum, when the primary user or spectrum quality deterioration occurs, the secondary users need to change the spectrum, which is called as the spectrum mobility. The new handoff is called as the spectrum handoff. Among the key technologies in Cognitive Radio Networks, spectrum handoff has received extensive concern from both academia and industry. Switching request strategy based on queuing theory is put forward for non-real-time data services, and blocking probability, outage probability and channel utilization rate are studied and simulated. According to the simulation analysis of the spectrum handoff, compared with the non-handoff strategy and reservation channel strategy, outage probability and channel utilization efficiency of the secondary users based on switching request queuing mechanism are both improved, and it can guarantee the smooth spectrum handoff.