1. An automatic focusing method in a high-noise environment, applicable for determining a focusing object distance between a digital image device and at least one object to be photographed, comprising: taking pre-photographed images at different object distances; loading the pre-photographed images; superposing the pre-photographed images respectively to generate a composite image; calculating an object distance corresponding to the composite image; calculating a high-frequency signal of at least part of pixels in the composite image; and determining the focusing object distance for the object to be photographed with the high-frequency signal and the corresponding object distance of the composite image as reference data.