The invention belongs to the field of preparation of metal materials, and particularly relates to a preparation method of an Al-40%Zn alloy twined dendritic crystal. According to the preparation method, the design that an Al-Zn alloy with high Zn content (40% Zn) is selected, a directional solidification technology is adopted, a high directional solidification drawing rate (900-1100[mu]m/s) is adopted, and a convection flow is formed in fusant during directional solidification, so that the Al-40%Zn alloy twined dendritic crystal is successfully prepared. According to the preparation method disclosed by the invention, the Al-40%Zn alloy is selected as the alloy system for preparing the twined dendritic crystal, and the alloy system selected in the method is different from an Al-Zn alloy system with low Zn content (30% or below) in a research report; and the component selection is not reported, so that technical bias is overcome.