The invention relates to a way to produce biological diesel oil through interesterification. The invention is to put animal oil (or vegetable oil) or ester and low-carbon alcohol into the reactor which is equipped with ultrasonic emission device and let them react under proper conditions. The invention can substantially increase the mass transferring process between alcohol and ester so as to shorten the reacting time and increase the transformation efficiency. Under malacopoeous conditions the invention also has very high transformation efficiency. Compared to the present technology, the invention has many advantages such as simple procedures, malacopoeous conditions, high transformation efficiency and fewer by-products. It can be used to produce biological diesel oil by different kinds of animal oil (or vegetable oil) or esters.