Abstract: Based on the classic Coluomb friction law, the maximum tensile stress criterion, the maximum compressive stress criterion and the fuzzy theory of fuzzy mathematics, the paper puts forward for the first time that the three kinds of masonry failure models called shear-friction, shear-compression and diagonal compression models under the shear-compression loading, which can be divided into two failure regions, namely the shear-friction and shear-compression failure region as well as the shear-compression and diagonal compression failure region. By adopting the weight function to combine the classic failure theory with the corresponding failure model, the paper presents the formula of the shear strength of masonry and simplifies it. The results of contrast indicate that the calculated curves are in good agreement with experimental results. Meanwhile, in the view point of some questions existing in ‘Code for design of masonry structures’ and ‘Code for seismic design of building structures’, the paper puts forward the design formulae of the static and seismic shear strength of masonry based on failure region theory. The computed results indicate that the formulae are not only simple and safe, but also improve the formulae of current design codes and can be used to design tall masonry structures.