  The method for calculation of the correlation functions of the Ising-type
systems with short-range interaction and with arbitrary value of spin is
developed within cluster approximation. For the Ising model (spin $S^z=\pm1$)
the expressions for pair and ternary correlation functions within two-particle
approximation in $\set{q}$-space are obtained for the hypercubic Bravais
lattices. In the 1D case the exact expressions for them in the site space is
obtained as well. On the basis of the Glauber equation within two-particle
cluster approximation the longitudinal dynamical susceptibility
$\chi(\set{q},E)$ is found. In the 1D case and in the absence of external field
the expression for $\chi(\set{q},E)$ is exact. For the Emery-Blume-Griffiths
model ($S^z=-2,0,2$) within two-particle approximation the pair correlation
functions are calculated. The four-particle cluster approximation is used for
calculation of static susceptibility $\chi(\set{q})$ of $KD_2PO_4$
ferroelectrics.
