Abstract: To investigate the shear performance of Tibetan stone masonry, double-shear experiments along horizontal bed joints of 13 specimens (four groups in different compressing load) made of granites and earthen mortar were carried out. Through the test, the shear strength along horizonal bed joints of Tibetan stone masonry was obtained. Meanwhile the failure mechanism of bed joints was analyzed, and methods to estimate shear strength of Tibetan stone masonry through shear strength of bed joints were studies. The results showed that the shear failure mode of bed joints in Tibetan stone masonry was a ductile failure process in which the deformation of earthen mortar and interface separation were developing at the same time, and the ultimate mode was pure slip along the separating interface. A computational model of shear strength for Tibetan stone masonry was proposed based on statistical analysis of the test results and the results showed good agreement with the test data. Compared to hydraulic mortar, earthen mortar has a lower cohesion and friction coefficient. Through two theoretical models, the relationship between the bed mortar's shear strength parameters and the masonry's was analyzed, and experimental data of other researchers was used to verify the results. A calculation formula to estimate shear strength of Tibetan stone masonry based on data obtained by the double-shear test was proposed, and it can be referred to for studies on Tibetan stone masonry's shear performance.