Combination of quantitative X ray diffraction(QXRD) and the Rietveld method possesses more unexampled advantages over other methods in quantitative crystal phase analysis of clinker. However, there exist amorphous phases containing poorly crystallized and non crystal ones in clinker, resulting in the overestimated phase contents that must be corrected to obtain the real contents. Therefore, two internal standards, Al2O3 and ZnO, frequently used but obviously distinct in the linear absorption coefficient, were added into clinkers to calibrate the crystal phase contents under the same experimental conditions; and the comparison of their ability to calibrate was done. Results indicate that the fraction of amorphous phases in clinker is 32.3%(by mass) that is surprisingly high and thus ignorable, whereas other corrected crystal phase contents are 38.8% for C3S, 15.3% for C2S, 4.9% for C3A and 8.7% for C4AF, and Al2O3 shows the better ability to calibrate than ZnO does as an internal standard in quantitative phase analysis(QPA) of clinkers.