1. A three-dimensional printing method, adapted for printing a three-dimensional object, the three-dimensional printing method comprising: obtaining a plurality of layer objects of a three-dimensional model by performing a slicing process on the three-dimensional model and generating a plurality of two-dimensional images, corresponding to a slice plane, of each of the layer objects, wherein the layer objects comprise a first layer object and a second layer object adjacent to each other; stacking the first layer object and the second layer object to generate thickness stack information of a stack object when a comparison relationship between the two-dimensional image of the first layer object and the two-dimensional image of the second layer object matches a stack condition; and initiating a printing mechanism according to the thickness stack information to print the three-dimensional object associated with the three-dimensional model, wherein the step of stacking the first layer object and the second layer object to generate the thickness stack information of the stack object when the comparison relationship between the two-dimensional image of the first layer object and the two-dimensional image of the second layer object matches the stack condition comprises: after obtaining the first layer object and the second layer object by performing the slicing process, determining whether a coverage of the two-dimensional image of the second layer object is larger than or equal to a coverage of the two-dimensional image of the first layer object; and after obtaining the first layer object and the second layer object by performing the slicing process, stacking the first layer object and the second layer object to generate at least one combined thickness and at least one combined control code file of the stack object only when the coverage of the two-dimensional image of the second layer object is larger than or equal to the coverage of the two-dimensional image of the first layer object, wherein the step of initiating the printing mechanism according to the thickness stack information to print the three-dimensional object associated with the three-dimensional model comprises: adjusting irradiation intensity of a light source into a first value according to the at least one combined thickness; and adjusting the irradiation intensity of the light source into a second value according to the at least one combined thickness and generating the stack object to have multiple thicknesses on a movable platform while moving the movable platform only once.