Disclosed in the present invention are a crystal form of monomethanesulfonate of a deuterated 3-(4,5-substituted aminopyrimidine)phenyl compound as represented by formula I, and a preparation method therefor. The crystal form is highly stable, can be used for treatment or prevention of diseases or conditions by means of epidermal growth factor receptors (EGFRs) in some mutation forms, can effectively inhibit the growth of a variety of tumor cells, and have an inhibiting effect on other proteases of EGFR and Her families, and thus can be used for preparing antitumor drugs.