A method for controlling an X-ray dose of a CT scan includes: setting an initial X-ray dose； performing a first CT scan with the initial X-ray dose to obtain an initial scan image； setting a region of interest (ROI) in the initial scan image； calculating an subsequent X-Ray dose with image values of the ROI in the initial scan image； perform an additional CT scan with the calculated subsequent X-Ray dose to obtain an average image； before receiving an end instruction, repeating the following operations: recalculating an subsequent X-Ray dose with image values of the ROI in the average image and performing an additional CT scan with the calculated subsequent X-Ray dose to obtain a new average image； and saving the average image when receiving the end instruction.
