Abstract: A system that uses Moiré fringe to detect the beam wander caused by atmospheric turbulence is presented. This system features tiny length and angle detection. The tiny angle of the beam wander was detected by using the Moiré fringe and amplified in the mode of fringe. The widest fringe obtained in the atmospheric turbulence was analyzed, and the width of the fringe was compared with the resolution of sophisticated CCD. Moiré fringe subdividing technique was used when the resolution of the CCD was not sufficient. The optical signal of the fringe was converted to the electric signal by a proper circuit, and the phase variation was converted to the pulse-width variation. The high frequency pulse was inserted into the formed square wave and the highmultiplyingpower subdivision was attained by measuring the numbers of the pulse. The high resolution can be achieved by this method which can make detection precision of the system reach 0.025μrad.