The invention relates to a composite developing thermosensitive gel embolizing agent as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, preparing a mixed aqueous solution of an anticancer active substance, a thermosensitive material and a developing agent into composite developing thermosensitive gel; secondly, forming a composite developing thermosensitive gel embolizing agent by the composite developing thermosensitive gel and a coagulant on the scene, wherein the thermosensitive material is hydroxyl C1-4 alkyl cellulose, Pluronic, alginate or a mixture of the substances; the anticancer active substance is arsenic trioxide, docetaxel, cisplatin, carboplatin, nedaplatin, oxaliplatin, lobaplatin, miriplatin, siRNA or a mixture of the substances; the developing agent is a water-soluble developing agent of iodixanol, ioversol or iohexol and the like. The preparation method disclosed by the invention is simple and convenient, is suitable for industrial large-scale production, is particularly suitable for preparing an embolizing agent which is biodegradable and good in biocompatibility and is used for hemorrhagic diseases, and is especially suitable for preparing the composite developing thermosensitive gel embolizing agent for treating liver cancer, kidney cancer, lung cancer, prostate cancer, uterine myoma or splenic tumor and the like.