A transition area, which appears in the transformation from a metastable phase to a stable one during the crystallization of Ni-33at% Zr amorphous alloy, had been investigated by means of TEM. From the lattice image, it can be seen that the unstable phase corresponds to fringes with broad spacing or alternate between broad and narrow spacings, the stable phase corresponds to a single kind of fringes with narrow spacing, but for the transition area the arrangement of fringes with broad or narrow spacing is random and shows no regularity. In addition, for this area, the electron diffraction pattern exhibits no translation summetry. The pattern can be seen as one of the transformation process between the unstable phase and the stable one. Distributions of the diffraction intensities of the transition area are simulated by means of models with identical atomic planes but various packing spacings, the result agrees with the actual intensity distribution very well.