  We propose a new variational method for describing nuclear matter from
nucleon-nucleon interaction. We use the unitary correlation operator method
(UCOM) for central correlation to treat the short-range repulsion and further
include the two-particle two-hole (2p2h) excitations of nucleon pair involving
a large relative momentum, which is called 'high-momentum pair'(HM). We
describe nuclear matter in finite size with finite particle number on periodic
boundary condition and increase the 2p2h configurations until we get the
convergence of the total energy per particle. We demonstrate the validity of
this 'UCOM+HM' framework by applying it to the symmetric nuclear and neutron
matters with the Argonne V4$^\prime$ potential having short-range repulsion.
The nuclear equations of state obtained in UCOM+HM are fairly consistent to
those of other calculations such as Brueckner-Hartree-Fock and auxiliary field
diffusion Monte Carlo in the overall density region.
