  We study in this paper bond distortion effect on electric polarization in
spiral multiferroic magnets based on cluster and chain models. The bond
distortion break inversion symmetry and modify the $d$-$p$ hybridization.
Consequently, it will affect electric polarization which can be divided into
spin-current part and lattice-mediated part. The spin-current polarization can
be written in terms of $\vec{e}_{i,j}\times(\vec{e}_{i}\times\vec{e}_{j}) $ and
the lattice-mediated polarization exists only when the M-O-M bond is distorted.
The electric polarization for three-atom M-O-M and four-atom M-O$_{2}$-M
clusters is calculated. We also study possible electric ordering in three kinds
of chains made of different clusters. We apply our theory to multiferroics
cuprates and find that the results are in agreement with experimental
observations.
