Software aging related failures can be prevented by applying software rejuvenation technology. But the restart operation in the software rejuvenation phase makes the system unable to provide services, which leads to system unavailability. The software rejuvenation model with pre-start technology is therefore proposed to reduce downtime and improve availability by switching between active copy and backup copy, which can substitute for restart operation and resolve unavailability problem. First of all, the rejuvenation operation of model with pre-start technology is described and improvements on the conventional model are presented. Second, the model availability is calculated by Markov Regenerative process. And finally, according to the experimental results, current model proves to be more available than the conventional one.