The invention discloses a preparation method for transformer oil modified by concentrated nano titanium oxide liquor. The preparation method comprises the following steps: (1), with cyclohexane and triethylamine as solvents, preparing tetrabutyl titanate liquor; (2), adding oleic acid to the tetrabutyl titanate liquor and uniformly mixing, and reacting for 12-72 hours at 150-180 DEG C to obtain a dispersion liquid of titanium oxide; (3), obtaining a series of concentrated titanium oxide liquor with different concentrations by changing a proportion of the tetrabutyl titanate liquor to the oleic acid; and (4), adding the concentrated titanium oxide liquor obtained in the step (3) into the transformer oil, uniformly mixing and carrying out ultrasonic treatment to obtain the transformer oil modified by the concentrated nano titanium oxide liquor. According to the preparation method, drying for the nano titanium oxide particles is omitted, the hard-agglomeration among the titanium oxide particles is effectively avoided and the dispersion of the titanium oxide particles is relatively good, so that the dispersion phase of the titanium oxide in the transformer oil is of a true nanoscale, the nano modified transformer oil also has excellent long-term stability, and the heat-conducting property of the transformer oil is also improved.