An important concept in multidimensional (nD) systems and signal processing is that of equivalence of systems, which is closely related to equivalence of multivariate (nD) polynomial matrices. By exploiting recent results on nD polynomial matrix factorizations, this paper presents several new results on the reduction by equivalence of a given nD polynomial matrix to a simpler form. In particular, the new results work for both 2D and nD (n > 2) cases. The paper also discusses equivalence of nD polynomial matrices that are not of normal full-rank, which have received little attention in the past.