In Integrated Modular Avionics (IMA) architecture, the definition of system functions is different from the definition of task-oriented distributed computing in the previous joint architecture.The redundancy of functional applications on IMA platform usually represents the redundancy of system functions.In order to determine the redundancy of the functions of the airborne system, four variables are introduced, which are the type of application software, the general processing resource module, the IMA platform chassis and the functional application software redundancy.A task reliability evaluation method is proposed, which can set dependent variables and feedback adjustment in turn.It can scientifically design the redundancy of functional application software in IMA architecture system, which provides a new way to analyze the redundancy of system function in IMA architecture.