The present invention relates to a slightly acidic environment-sensitive and ketal-linked gefitinib axially substituted silicon phthalocyanine complex and a preparation method therefor and a medical use thereof. In particular, the present invention relates to a silicon phthalocyanine-gefitinib complex as shown in general formula (I) and a preparation method therefor and a pharmaceutical composition containing the complex, and the use thereof as a photosensitiser, especially the use in the treatment of cancers, wherein the definition of each substituent in general formula (I) is the same as that in the description. In a normal tissue environment, due to the interplay of the silicon phthalocyanine group and the gefitinib group, the complex has a lower cytotoxicity. However, in the extracellular slightly-acidic environment of the tumour tissue, ketals hydrolyse and the fragments of the hydrolysate, i.e. silicon phthalocyanine, exhibit an extremely high photosensitive activity, while another hydrolysate, i.e. a gefitinib derivative, can be used as an inhibitor of epidermal growth factor receptor (EGFR) tyrosinase for inhibiting tumour growth. The complexes can be prepared into photodynamic therapeutic and chemotherapeutic double-efficacy anticancer drugs targeting both the tumour extracellular slightly-acidic environment and the EGFR tyrosine kinase.