Abstract: The solid base catalyst K2O/C was prepared by the vacuum impregnation method. The orthogonal experiment was employed to optimize the preparation condition.The results indicated that the optimal reaction parameters were carbon carrier with average pore size 2.87 nm, K2CO3/C mass ratio 0.5, catalyst calcination temperature 450 ℃, and calcination time 2 h. The prepared catalyst K2O/C was adopted to catalyze the transesterification reaction of cellulosic oligosaccharide esters from cellulosic oligosaccharide and methyl oleate under ultrasonic assistance. The optimum conditions were obtained as follows: the ultrasonic frequency 20 kHz, the ultrasonic power 150 W, treatment time 15 min, the mole ratio of methyl oleate to cellulosic oligosaccharide esters 2:1, the mass fraction of K2O/C 5%, the reaction temperature 125 ℃, and the reaction time 2 h. Under these conditions, the yield of cellulosic oligosaccharide esters reached 85.6%. The synthesized product has esterification degree 18.8%, HLB 9.89, surface tension 32.1 mN/m, and the emulsifying ability 28.1%. The product showed good performance on surface tension, emulsion and stability in hard water.