Partial hydrogenation is an effective way for improving the performance of polyunsaturated fatty acids and polyunsaturated fatty acid esters. However, trans-isomers generated in the hydrogenation reaction, which would lead to the poor quality of hydrogenated oils and fats. It is significant to study the reducing of trans-isomers generation during the hydrogenation of fatty acid and its esters. The hydrogenation mechanism and the reason of trans-isomers generation have been introduced. On the base of this, it has reviewed the progress of reducing of trans-isomers in terms of hydrogenation method, active components, metal modifier, support materials and preparation method of catalyst. The influence rules about formation of trans-isomers were analyzed and summarized. Furthermore, the reducing methods of trans-isomers generation were proposed.