As a fast and accurate SW simulation model,we present a model called fast timed SW model .The model enables fast simulation by native execution of application SW and OS.It gives simulation accuracy by timed SW and HW simulation.When building fast timed SW models,we need to solve two problems:(1)how to enable timing synchronization between the native execution and HW simulation and (2) how to obtain the portability of native execution (that needs multi-tasking from simulation environments to emulate its multi-tasking operation) on different simulation environments (that give different types of multi-tasking). In this paper, to enable the synchronization, we present a synchronization function. To enable the portability, we present an adaptation layer called simulation environment abstraction layer. We present our case studies in building fast timed SW models.