Abstract: This paper proposes a failure diagnosis method,called failure-function analysis method(F-FAM),for an attitude control system in a carrier rocket.It consists of two parts:failure function tree analysis andfailure mode analysis.The latter is an extension to the former.In failure mode analysis,the discussioncentres on estimation of failure model parameters of every link in the attitude control system.Finally.some examples are given to verify the feasibility and rapidity of this method.