This paper aims to study the uncertainty of the MDOF structural dynamic response, taking
not only the interval characteristics of structural physical parameters and geometric dimension, but
also the interval characteristics of applied load simultaneously . By means of the description of the
interval parameters of uncertain structure with affine forms, the interval structural dynamic equation
is studied, and an improved affine arithmetic based on interval division is presented, where
correlations between the interval elements in eigenvalue and responses equations are considered,
independent uncertain parameters are transformed to affine forms, and the solution of eigenvalue and
response equations are transformed into the corresponding certain ones. With general affine
arithmetic, the eigenvalue of each order and response bounds are determined by searching for the
maximum and minimum in the solutions. Finally, some mathematical examples and a further
engineering application confirm the feasibility and validity of this approach.