A method for searching a printing frequency to display a 3D picture includes breaking an image into strips and using NumLen lenses to form a NumLen-1 image cycle. After the NumLen-1 image cycle is formed, a quantity of images of the image cycle is defined to be dpi/lpi, where dpi is dot per inch of a printer and Ipi is lens per inch of a lenticular lens. Therefore, a quantity of the image per inch is arrived.