The invention relates to a preparation method of TDI isocyanurate. Raw materials comprise: TDI, monohydric alcohol, a solvent, an anti-oxidant, a catalyst and a terminator. The method of the invention improves the performance of isocyanurate by processes of monohydric alcohol modification, and multi-step addition of the catalyst and the solvent at an appropriate temperature. In the preparation process, the catalyst and the solvent are added in batches under the condition that the NCO% and the viscosity are controlled simultaneously; the solid content of each step is adjusted; the finally prepared TDI isocyanurate is low in free TDI content, high in xylene tolerance, small in product color number, high in performance stability, and good in product application performance such as the drying property, polishing property and delustring property of paint films, and compatibility between the isocyanurate and other components.