The invention discloses a prefabricated and assembled power transmission line tower footing and a construction method of the tower footing. The prefabricated and assembled power transmission line tower footing comprises a bottom plate and a column body, wherein the column body is connected with the bottom plate by a plate and column connecting piece; the bottom plate is formed by splicing bottom plate units; the column body is formed by splicing column body units. The construction method comprises the steps of splicing the bottom plate unit arranged in the center of the bottom layer of the bottom plate and the plate and column connecting piece, then splicing the whole bottom layer of the bottom plate from inside to outside, and adjusting the bottom layer of the bottom plate to be horizontal; splicing the upper layer of the bottom plate or the bottom layer of the column body from bottom to top from the center of the bottom layer of the bottom plate until the column body is completely spliced, and adjusting the perpendicularity of the column body at any time in the splicing process. Therefore, the related working procedures such as formwork erecting of cast-in-place concrete, mixing, pouring, maintaining and the like can be omitted, and the structure of the tower footing can be spliced after a foundation pit is prepared, so that the labor intensity is remarkably lightened, and the construction period is shortened.