The refractive index matching liquids is used in the 3-D stress measurement by holographic interferometry,and the liquid will influence the stability of the optical system and the reconstructed image.So study on this problem is necessary.Based on theoretical analysis an experimental system was designed.After comparing the images reconstructed with holograms recorded before and after adding refractive index matching liquid and comparing phases of the reconstructed wavefront,the following useful results are obtained: refractive index matching liquids will reduce image reconstruction distance but do not zoom the image,and the liquid takes about 15 hours to become stable.