The crystal structure of K2ZnI4 is refined at 24 temperatures above and below the paraelectric-ferroelectric phase transition temperature by means of X-ray diffraction to reinvestigate the mechanism of the phase transition in more detail. The temperature dependence of the translation of K(1) and K(2) along the b-axis and the rotational angle of the ZnI4 tetrahedron about the axis nearly parallel to the a-axis is obtained by the structural analyses. It is concluded that the mechanism of this phase transition is not the order-disorder type but the displacive one. The temperature variation of the anisotropic temperature parameter U-22 of K(1), K(2), I(1) and I(2) is coincident with the theoretical prediction for the displacive type phase transition proposed by Fujii and Matsubara [Prog. Theor. Phys. 78 (1987) 177].