In this paper, a new exact order reduction approach will be proposed for Roesser state-space model of multidimensional systems based on multiple eigenvalues. Comparing with the existing eigenvalue trim reduction approach taking into account one eigenvalue of some certain sub-block, the new exact order reduction approach is able to simultaneously consider multiple eigenvalues of different sub-blocks. As a consequence, the existing eigenvalue trim reduction approach can be viewed as a special case of the new proposed approach. Moreover, corresponding examples are given to illustrate the details as well as the effectiveness of the proposed approach.