Abstract: The introduction of new noise symbols causes error amplification in affine arithmetic inevitably. To avoid this disadvantage, this paper presents a modified affine arithmetic in matrix form for bounds computation of functions. The modified affine arithmetic does not introduce new noises during multiplication operation of affine variables, and it can obtain compacter bounds compared with conventional affine arithmetic. The formulas computing processes and the validity of proposed method are demonstrated by an example. The affine form of bounded uncertain variables and modified affine arithmetic are used to calculate response bounds of uncertain system. The simulations show that, the proposed approach can obtain closer response bounds than interval arithmetic and conventional affine arithmetic.