In order to measure the curves of distance and output voltage for eddy current sensor, a speckle correlation method is proposed. Firstly, the linear interval is measured by the displacement platform with precision of 5um. Secondly, congestion sampling is taken out in the linear interval, the speckle pattern under different distance is captured by the micro-imaging system and more precision curves are obtained with displacement calculated by the speckle correlation method. The precision of measurement is analyzed and the influence of speckle size on measurement is also discussed. The micro-imaging system with magnification of 64.5 is designed by combining an objective with 40 magnifications and a reading microscope with 20 magnifications. The experimental object is the 40 chromium and the results show that the proposed system can achieve high precision calibration for eddy current sensor with 0.09 μm precision and more precision can be obtained by changing the magnification of the imaging system.