The invention relates to a preparation method of sterol ester and in particular relates to an enzymatic synthesis method of phytosterol ester / phytostanol ester by utilizing ultrasonic enhancement. The method is characterized by comprising the following steps: 1) preparing a heterogeneous enzyme reaction system: weighing the phytosterol ester / phytostanol ester and fatty acid at a molar ratio of 1:(1.2-2), adding a reaction solvent, and adding enzyme and a molecular sieve; 2) performing enzymatic esterification with ultrasonic assistance: immersing an ultrasonic probe in a reaction solution, opening an ultrasonic wave generator, constantly radiating with ultrasonic wave for 0.5 to 3 hours under mechanical stirring, and continuously reacting for 4 to 10 hours under mechanical stirring after the radiation is completed; and 3) removing the fatty acid with ultrasonic assisted saponification to obtain the product. According to the method, the enzymatic esterification reaction time can be remarkably shortened, the usage of enzyme can be reduced, and the saponification speed of excessive fatty acid can be accelerated, so that the efficiency of separation and purification can be improved, and the obtained phytosterol ester / phytostanol ester product has the characteristics of light color, high purity and safety without contamination.