Critical shear span ratio of bend and shear cracking of brick wall is studied in order to determine and control configuration of bend and shear failure of masonry bearing walls subjected to horizontal action. The concept of critical shear span ratio between bend and shear cracking is set forth firstly, and the analysis principle of critical shear span ratio of plain brick wall is dissertated. Furthermore, different parameters of average axial compressive stress and shear strength etc. of brick wall are adopted in the range of storey number, height and material strength, and critical shear span ratio of rectangular plain brick wall is calculated by means of FEM. The analyses indicate that critical shear span ratio of plain brick wall in masonry structures is 0.35∼0.5; the influence of average axial compressive stress and shear strength of masonry wall on critical shear span ratio is trifling; critical shear span ratio is used to not only determine configuration of initial cracking but also deduce final elasto-plastic failure and provide a basis for controlling failure configuration of masonry walls.