Abstract: The aircraft real-time SAR imaging system is fixed on the plane, and consists of several embedded signal processing boards and a host computer connected by CPCI industrial bus and CAB bus of Coreco, Inc The host computer plays a crucial role in the whole system, responsible for real-time data sampling, storing and displaying, and the most important, the host module must provide a firm real-time computing environment to guarantee the priority-base scheduling of these tasks Instead of using readily available proprietary DSP packages and expensive commercial real-time operating systems （RTOS） such as QNX or VxWorks, an alternative solution is investigated: using a low cost PC and RT-Linux-a compact real-time extension to Linux to construct the host module of SAR imaging system The architecture of the host module is introduced, and several essential aspects of the design are addressed: a novel scalable hierarchal communication framework between multi-DSP and host module and a hybrid task set under RT-Linux, which consists three hard real-time periodical tasks and several soft real-time tasks The real-time mechanism of RT-Linux is analysed In order to illustrate the feasibility of RT-Linux based solution, a set of experiments to decide the dispatch （scheduling） resolution of both Linux and RT-Linux are constructed and the results of comparison are given with figures