Pd/C catalysts was prepared by impregnation and the variation of soy lecithin’s iodine value after hydrogenation was studied. The characterization of catalysts was analyzed by using microspecrtoscopy (TEM). The results showed the optimum preparation condition was as follows: when carbon was pretreated with 10% HNO3 solution, impregnated 2h in 3.5mg/mL H2PdCl4 solution at 40℃, then reduced 5h in 30% formaldehyde solution at 80℃, solution pH value 1～2, Pd/C catalysts were dried in 80℃ vacuum condition. The Pd particles size was 7.8nm. After Pd/C catalysts hydrogenated, soy lecithin’s iodine was down to 18.6gI/(100g). The results showed solution pH value effected catalysts activity largely. The smaller Pd particles size was, the stronger catalyst activity was.