The invention discloses a synthesizing method of fluomethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, which comprises the following steps: 1) reacting 1,1,1,3,3,3-hexafluorine-2-propanol and ,3,5-trioxymethylene or oligoformaldehyde and Lewis acid chloride to generate chloromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether as intermediate and HOAlCl2 as by-product; adding 6N HCl to disintegrate to remove by-product HOAlCl2; 2) reacting chloromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether and fluorination agent and solvent to produce the product; improving the selectivity of intermediate; removing by-product easily.