Based on the nearly free-electron approximation, we have investigaed the te
mperature (T) dependence of spin-polarized tunneling in the magnetic tunnel
junction with an asymmetrical barrier, with emphasis on the variation of m
olecular field with T in the same way as that of surface magnetization. It
is found that the Slonczewski model can describe well the T dependence of s
pin-polarized tunneling, while the Julliere model only describes the T depe
ndence of JMR qualitatively, but does accurately that of the difference of
tunneling conductance between the parallel and antiparallel alignments for
the magnetizations of FMs; Differing from the previous finding, we find the
electron spin polarization is not strictly proportional to the surface mag
netization, for the former decreases with the increasing T more rapidly tha
n the latter does.