Aiming at the problem of dependability validation in the distributed realtime systems, the universal fault model is established, which is classified into four groups: memory fault, CPU fault, communication fault, and service fault. A software implemented fault injection architecture (SWIFIA) for the distributed realtime systems is proposed, which is classified into three levels: target system, communication network, and software implemented fault injection system (SWIFIS). The SWIFIS is designed with three parts: software implemented fault injector, data collection module, and fault data analysis module. The process of software implemented fault injection based on the architecture is illustrated. SWIFIS is implemented and analyzed with experiments. The major faults detected in the experiments are communication faults, memory faults, and CPU faults while the coverage rates were 37.68%, 15.47%, and 15.17%, respectively. The experimental results demonstrate that this architecture is suitable for the applications under distributed realtime environment. They offer theoretical base and evidence for further research of software dependability validation.