A mesylate salt of a compound represented by formula (I) and preparation method therefor, a pharmaceutical composition containing the salt, and an application of the salt in the treatment of activated EGFR mutant- or drug-resistant mutant-mediated diseases, especially cancer, in mammals, particularly humans. The mesylate salt of the compound represented by formula (I) has high bioavailability in animals, can better inhibit the growth of transplanted tumors in animals, and demonstrates desirable safety.