Abstract: Applying redundant architecture is an important way to improve and promote the reliability of computer in space. The redundant architecture of space computer can be organized in different forms depending on the combination of software and hardware resources. Recently most comparisons among different redundant architectures in engineering are performed only by rough analysis,not in quantitative way,especially for the relatively complex architectures. In this study,six typical redundant architectures(dual-unit with cold standby,dual-unit with hot standby,TMR,re-configurable TMR,2+1 triple-unit,and quad-unit)are investigated,the Markov chain models are established and the formulas of reliability are deduced respectively. Reliability of the architectures is calculated,analyzed and compared based on a virtual five-year space task. The simulation results indicate that a solution with cold standby resource can obtain higher reliability. Moreover,the ability of a fault unit to recover easily and quickly can greatly improve the system reliability.