  The boundary of phase separation of the two-dimensional t-J model is
investigated by the power-Lanczos method and Maxwell construction. The method
is similar to a variational approach and it determines the lower bound of the
phase separation boundary with $J_c/t=0.6\pm 0.1$ in the limit $n_e\sim 1$. In
the physical interesting regime of high T_c superconductors where $0.3<J/t<0.5$
there is no phase separation.
