Objective To evaluate the outcomes of bevel-down phaco-chop and study the mechanism which results in the loss of corneal endothelium in phacoemulsification. Methods 251 eyes accepting phacoemulsification were divided into two groups. The technique of bevel-down phaco-chop was performed on 127 eyes in group A. The nucleus density grade was Ⅱ in 28, Ⅲ in 69, and Ⅳ-Ⅴin 30 eyes. The other 124 eyes were divided into group B and on which the traditional technique of bevel-up phaco-chop was performed. The nucleus density grade wasⅡin 31, Ⅲ in 65, and Ⅳ-Ⅴin 28 eyes. The differences of accumulated energy complex(AEC) and corneal endothelium loss (CEL) over 6 months postoperation were compared between the 2 groups. Results In group A, the AEC was 2.7±0.5, 11.9±2.1 and 30.2±8.1 seconds; the CEL was (5.1±0.6)%, (8.9±0.4)% and (12.5±1.6)% in eyes with grade Ⅱ, Ⅲ and Ⅳ-Ⅴnucleus density respectively. In group B, the AEC was 2.6±0.4, 12.2±2.5 and 31.7±8.9; the CEL was (5.0±0.5)%, (11.2±0.8)% and (20.6±1.4)% respectively. The CEL had no difference in the eyes with grade Ⅱ nucleus density（P＞0.05）, but had differences in the eyes with grade Ⅲ and Ⅳ-Ⅴnucleus densities between the 2 groups（P＜0.05）. Conclusion Bevel-down phaco-chop can reduce damage to corneal endothelial cells and is more useful in hard cataract phacoemulsification.
