1. A method for dose modulated X-ray scanning, the method comprising: setting a target image quality standard for a scanning region; determining a reference data level for the scanning region; calculating a theoretical X-ray scanning dose for the scanning region, according to the target image quality standard and the reference data level; calculating an X-ray attenuation difference between each data level corresponding to the scanning region and the reference data level, according to the theoretical X-ray scanning dose; identifying any one of the data levels corresponding to the scanning region, whose X-ray attenuation difference with the reference data level is higher than a threshold, as a target to be de-noised; and performing a noise reduction for the target to be de-noised.