A method for homogenizing an illumination energy in multiple-projector large-scale mask projection 3D printing to reduce illumination unevenness, the method comprising the steps of: Step 100: using at least two projectors as a light-source for mask projection, and locating the projectors to be adjacent to each other so that there is an overlapped area between the projection areas of the projectors, wherein the two projectors project two images with the same size and resolution but with different pure colors, a first color and a second color, selected from the three primary colors, and the overlapped area between the projection areas of the projectors has a third color; then, using a camera to capture an image of the projection areas and the overlapped area, and analyzing the image using a computer, wherein the height and width of the overlapped area are denoted as H 0 and W 0 respectively; Step 200: based on the information of the height H 0 and the width W 0 of the overlapped area, segmenting a preprocessed slice which is obtained from the captured image to create two slices which are denoted as P 1 and P 2 respectively; recording the width W 1 and W 2 and the H 1 and H 2 of the two slices P 1 and P 2; and then generating two corresponding gray leveled pictures P 3 and P 4 having the same size and resolution with the two slices; Step 300: measuring the output energy at the same position on a printing area with discrete gray levels; by analyzing the measured data, obtaining a mapping function T[r(x,y)] by using curve fitting, the mapping function defining a relation between the output energy and the gray level r(x, y) at each position (x, y); and based on the mapping function T[r(x,y)], optimizing the generated pictures P 3 and P 4 using gray level interpolation; and Step 400: fusing the pictures P 3 and P 4 treated above with the two slices P 1 and P 2 to generate a series of 3D printed slices with energy homogenization. Step 100: using at least two projectors as a light-source for mask projection, and locating the projectors to be adjacent to each other so that there is an overlapped area between the projection areas of the projectors, wherein the two projectors project two images with the same size and resolution but with different pure colors, a first color and a second color, selected from the three primary colors, and the overlapped area between the projection areas of the projectors has a third color; then, using a camera to capture an image of the projection areas and the overlapped area, and analyzing the image using a computer, wherein the height and width of the overlapped area are denoted as H 0 and W 0 respectively; Step 200: based on the information of the height H 0 and the width W 0 of the overlapped area, segmenting a preprocessed slice which is obtained from the captured image to create two slices which are denoted as P 1 and P 2 respectively; recording the width W 1 and W 2 and the H 1 and H 2 of the two slices P 1 and P 2; and then generating two corresponding gray leveled pictures P 3 and P 4 having the same size and resolution with the two slices; Step 300: measuring the output energy at the same position on a printing area with discrete gray levels; by analyzing the measured data, obtaining a mapping function T[r(x,y)] by using curve fitting, the mapping function defining a relation between the output energy and the gray level r(x, y) at each position (x, y); and based on the mapping function T[r(x,y)], optimizing the generated pictures P 3 and P 4 using gray level interpolation; and Step 400: fusing the pictures P 3 and P 4 treated above with the two slices P 1 and P 2 to generate a series of 3D printed slices with energy homogenization.