The excised rat kidney slices were investigated using the diffraction enhanced imaging (DEI) method under the different FWHM of the rocking curve with 33.7keV x-ray, for the first time. The narrower FWHM of the rocking curve is used in the DEI imaging, the finer structure of the sample can be clearly distinguished and more details can be seen in the DEI image. Tuning the rocking curve width between 1.7μrad and 0.31μrad was done with small loss of peak intensity using a Si (220) double-crystal analyzer. The reason related with the influence of the FWHM of the rocking curve to the contrast resolution of DEI method is discussed. For the thin sample, how small deflected angle can be distinguished determines how small difference of density can be distinguished in the DEI imaging.