1. A method for displaying three-dimensional integral images by a first mask disposed to front on a three-dimensional object and having a blocking region and a transmission region, the first mask passing images of the three-dimensional object through the transmission region of the first mask, a first lenslet array closely contacted to a side of the first mask, through which the images of the three-dimensional object from the first mask pass, a two-dimensional detection unit receiving and storing the images from the first lenslet array, a second lenslet array disposed separately from the first lenslet array, through which the images from the two-dimensional detection unit pass, and a second mask disposed separately from the first mask and closely contacted to a side of the second lenslet array and having a blocking region and a transmission region, comprising: transmitting, by the first mask, the images from the three-dimensional object to the first lenslet array, wherein the images pass through the transmitting region of the first mask but are blocked by the blocking region of the first mask in a way of a time division multiplexing; transmitting, by the first lenslet array, the images from the first mask to the two-dimensional detection unit; receiving and storing, by the two-dimensional detection unit, the images from the first lenslet array; transmitting, by the second lenslet array, the images from the two-dimensional detection unit to the second mask; and transmitting, by the second mask, the images from the second lenslet array to a space for displaying, wherein the images pass through the transmitting region of the second mask but are blocked by the blocking region of the second mask in a way of a time division multiplexing, thereby displaying the three-dimensional image in the space, wherein the images are transmitted through in order of the first mask, the first lenslet array, the two-dimensional detection unit, the second lenslet array and the second mask, to the space for displaying.