Abstract: Rietveld method is an efficient way to find out the crystal structure and micro-structure of solids. Data treatment strategy has great effect on the its results. In this paper, the effects of truncating angle on its results were sindied systematically. It was found that the site coordination of heavy atoms can be obtained at medium diffraction angle while it needs more high angle data in order to determine the cell parameters and site coordination of light atoms. With the increase of data at high diffraction angular range, the profile parameters almost keep constants; the changes of numerical criteria of fit(including D-wd) are etermined by background parameters.

Key words: numerical criteria of fit, Rietveld method, truncating angle, crystal structure