  We have combined the complex momentum representation method with the Green's
function method in the relativistic mean-field framework to establish the
RMF-CMR-GF approach. This new approach is applied to study the halo structure
of $^{74}$Ca. All the continuum level density of concerned resonant states are
calculated accurately without introducing any unphysical parameters, and they
are independent of the choice of integral contour. The important
single-particle wave functions and densities for the halo phenomenon in
$^{74}$Ca are discussed in detail.
