In this paper,the optical correlation recognition in a Sagnac interferometer wit h second-order correlation is analyzed and demonstrated theoretically and exper imentally.The intensity distribution is recorded from the Sagnac interferometer irradiated by a pseudo-thermal light source.The intensity correlated interferen ce is obtained with the recorded intensity and a further Fourier transform on th e correlation results is executed.In the experiment,the distance from the optica l axis of the object was measured as 387μm and 486.5μm by the first order br ight spots.The change of the the object′s lateral displacement was measured as 97.5μm,which was a small measurement error for 2.5μm.In this paper,the hundr ed-micron optical correlation recognition is realized by observing the light sp ots of the output,and the distance of the object from the optical axis is measur ed.When the horizontal position of the object changes,the position of the primar y bright spot changes with it.The changes of the lateral displacement can be mea sured,and the measurement accuracy is higher.It is to be hoped that our results will be of value not only to the application of optical correlation recognition and medical but also to military fields.