This paper presents a solution for the state and unknown input estimator of linear MIMO systems with a structural approach. Compared to the classic Input-Output Decoupling problem, a systematic procedure is initially proposed for the analysis stage by analysing the finite and infinite structures of the modelled system from a structural approach. Afterwards, the observer is directly implemented from the original model at the synthesis stage in a graphical approach with some added terms, and can be represented by a Bond Graph model. The observer is tested by a particular and illustrative example which considers a real torsion-bar model.