1. A method for converting a Two-Dimensional video image into a Three-Dimensional video image, comprising: in a step A, performing a lifting wavelet transform on a current frame and a reference frame of a two-dimensional video image signal, respectively, to obtain high-frequency components and low-frequency component of the current frame, and high-frequency components of the reference frame, the high-frequency components comprise high-frequency components in three directions of horizontal, vertical and diagonal; in a step B, establishing triangular geometric models in the three directions of horizontal, vertical and diagonal, respectively, according to the high-frequency components of the current frame; in a step C, performing a motion search on the high-frequency components of the reference frame in the three directions of horizontal, vertical and diagonal, respectively, by using the triangular geometric models of the current frame, so as to obtain motion vectors in the corresponding directions, and calculating depth variations in the corresponding directions according to the motion vectors in the corresponding directions; in a step D, performing an interpolating operation on the triangular geometric models in the three directions of horizontal, vertical and diagonal, respectively, according to the depth variations in the corresponding directions, so as to obtain high-frequency depth graphs in the corresponding directions; and in a step E, completing a filtering reconstruction by performing an inversion wavelet transform on the high-frequency depth graphs in the three directions of horizontal, vertical and diagonal and the low-frequency component of the current frame, respectively, so as to construct a three-dimensional video image.