The invention relates to a preparation method of an initiating agent for synthesis of high polymers, in particular to a preparation method of emulsion type tert-butyl peroxyneo-caprate. The preparation method includes: adding tert-butyl hydroperoxide in alkaline solution, adding neodecanoyl chloride in the alkaline solution in dropwise mode, finishing adding of the neodecanoyl chloride in 40-120 minutes, stirring and reacting for 30-50 minutes, separating mother solution, and washing a reaction product to potential of hydrogen (pH) ranging from 5 to 7; mixing deionized water, an antifreezing agent, an emulsifying agent and an dispersing agent evenly to obtain water-phase solution; mixing the reaction product and the water-phase solution according to mass ratio of 1: (0.90-1.00), and stirring for 3-3.5 hours at the temperature of 0 DEG C to perform emulsifying synthesis. Content and yield of produces manufactured by the preparation method are improved greatly, the products are easy to store and transport. The preparation method of the emulsion type tert-butyl peroxyneo-caprate simplifies technological process, overcomes complicated requirements of reaction devices, and enables reaction to be performed under relatively temperate and safe conditions. Products yield can reach above 95%.