The rapid growth of KDP-type crystals mainly adopts the point seed rapid growth method. The three-dimensional point seed will inevitably lead to the pyramid-prism boundary, which affects the performance and quality of the crystals. In this paper, the traditional rapid growth of point seed method was improved by the designed platform, and the 70% DKDP crystal was successfully grown by the directional growth of point seed. Avoiding the pyramid-prism boundary of the growing crystals, slices were taken, of which the deuterium content, transmittance, laser damage resistance and optical homogeneity were tested. The results show that the deuterium content of the crystals meets the design requirements, the transmittance and laser damage resistance of the crystals are consistent with those of the crystals grown by the traditional rapid growth of point seed. The results of optical homogeneity show that there is no pyramid-prism boundary in the slices, which will guide the growth of large diameter 70% DKDP crystal.