The invention discloses a new anti-cancer drug intermediate which is a compound as shown by a formula III (IIIa or IIIb). A preparation method comprises the following steps: taking a 2-acetyl-4-formiate thiazole compound as a raw material, performing halogenating reaction, and then enabling the compound to react with triphenylphosphine, trimethyl phosphite and triethyl phosphite to prepare the intermediate. The compound as shown by the formula III can be further used for preparing the anti-cancer drug intermediate, for instance, the compound reacts with isobutyraldehyde through Wittig or Wittig-Horner to obtain a compound as shown by a formula I. The process is new as a whole, not only can the price of raw materials be reduced, but also the reaction condition is mild, the generated three wastes are fewer, and the industrial application is easy.