A mefatinib composition, related compounds, a preparation method therefor and use thereof. The mefatinib composition comprises mefatinib represented by formula (I) and a compound represented by formula (II) having a normalized percentage content of 1.0% or less but not zero. The mefatinib composition can be used to treat or prevent a variety of indications associated with EGFR and HER2 kinase functions, and the incidence of toxic response is small. The compound of formula (II) can be used, as a standard for related materials in mefatinib, for quality control of mefatinib active pharmaceutical ingredients or formulations.