The invention provides an assembling tool and an assembling method thereof. The assembling tool comprises a support; a pressure structure slidably arranged on the support along a preset direction, and comprising an operation part for driving the pressure structure to slide, and a pressure part connected to the operation part and sliding to a preset direction under driving force; a locating plate slidably arranged on the support along a preset direction, and sliding under the pressure of the pressure part; an adsorption structure fixed to the locating plate, and used for adsorbing an assembling object; and a base provided with a bearing surface, and a plurality of locating blocks slidably arranged on the bearing surface, wherein the locating blocks slide to preset positions to fixedly clamp an object to be assembled, and the preset positions are opposite to the adsorption structure so as to allow the locating plate to slide along a preset direction under pressure, and drive the adsorption structure to assemble the assembling object to the object to be assembled. The assembling tool is simple to operate, is helpful for improving assembling precision and efficiency, and furthermore reduces dull repetitive work.