Abstract: The micro stereovision systems with stereo light microscopes(SLM)have been applied to micromanipulation systems.There is a coupling connection between the two optical paths of a stereo light microscope. The coupling intension corresponds with two factors.The first one is the structure of a stereo light microscope,and the second is the position of a random object point in the view field of a stereo light microscope.A correlation function is proposed to describe the coupling intension of two optical paths for the quantity of correlation between the couple optical paths of a stereo light microscope.The quantified results are applied to the error analysis of an imaging model.Experiments show that correlation of optical paths of CMO-SLM is little more than that of G-SLM,and error should be considered when a pinhole model is used to analysing the correlation.