1. A method for inspecting uniformity of a critical dimension (CD) of a photo mask pattern, the method comprising: obtaining information for the CD of a pattern formed in the photo mask by precisely measuring the photo mask; obtaining a plurality of measurement images having the pattern by photographing the photo mask at a high speed: capturing respective pattern areas provided in the plurality of measurement images: calculating a gray level value of the pattern area; confirming an estimated value corresponding to a change of the gray level value based on the CD of the precision measurement; and confirming the uniformity of the CD at a measurement of high speed by checking a range the gray level value deviates from the estimated value.