Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk amorphous alloy (BAA) was prepared by arc melting and copper mold rapid casting. The crystallization process was tested by a heat expansion method, and the results were compared with that of the differential scanning calorimetry (DSC). The formation of the crystal nucleus and the crystal growth rule at the initial stage of crystallization was observed by high resolution transmission electron microscope (HRTEM). It is found that the relaxation process of the amorphous structure, glass transition, supercooled liquid region, starting temperature of crystallization and peak temperatures of the crystallization process which were tested by heat expansion are accordant with DSC results. The near-spherical nanocrystalline grains and crystal lattice stripes can be observed in HRTEM images. However, it is difficult to identify the tiny crystallization zone by HRTEM images at the initial stage of crystallization. The basic crystallization characters of the tiny zone can be observed expediently only by the fast Fourier transform (FFT) for the HRTEM image.