Abstract: Based on the Kirchholf diffraction theory, the slab imaging performances are studied for different negative refractive index deviating from -1, and the field patterns are drawn with MATLAB. The results show that when refractive index deviates from -1, the lightintensity distribution around the image point becomes asymmetric along z-axis, the fields are irregular and the satellite peaks occur. In addition, the aplanatic curvature radius r was found. The results show if the object point is put at the aplanatic point corresponding to the radius curved surface, the spherical aberration can be eliminated but the location of the image point is different from that of n=-1.