A new method has been explored to synthesize zeolite ANA crystals with regular icositetrahedron in aqueous media via transformation of zeolite Y under the conditions of low temperature, short reaction time, and without organic template. The products are perfect, almost 100% crystals. The samples prepared at different crystallization stages are measured by XRD, TEM, and SEM to investigate the transformation mechanism from zeolite Y to zeolite ANA. It has been demonstrated for the first time that the mechanism of forming a zeolite ANA polycrystal with sphere or shell morphologies is the in situ solid phase iso-structure transformation (Is-SPIST) of zeolite Y. The Is-SPIST mechanism is also supported by the results of steam-induced crystallization experiments and other assistant means, including the same Si/Al ratio, the same weight, the same particle size, and the same morphology before and after transformation of zeolite Y to zeolite ANA. It is also observed that a spherical or shell ANA polycrystal is constructed via the reconstruction from its exterior to interior, to form an ANA single crystal with a solid or hollow icositetrahedron. The main driving force of the reconstruction is considered to be the grain boundary energy existing between polycrystalline grains. This process also obeys the mechanism of in situ solid phase reconstruction (Is-SPR). Furthermore, the size and morphology of the zeolite ANA single crystal can be modified by surfactants.