The invention relates to a preparation method of titanium dioxide nano-particle modified transformer oil, and belongs to the technical field of preparation of the transformer oil in the power industry. The preparation method of the titanium dioxide nano-particle modified transformer oil comprises the following steps: 1, performing surface treatment on TiO2 nano particles to obtain surface-wrapped TiO2; 2, mixing the modified TiO2 nano particles with transformer oil by an ultrasonic or ball grinding method, so as to finally prepare the available TiO2 nano-particle modified transformer oil. The TiO2 nano-particle modified transformer oil obtained by the preparation method disclosed by the invention is excellent in heat conduction performance and electric property, and is high in long-term stability, and the stability and the reliability in the service period are guaranteed.