3 groups of 18 shear specimens were tested to investigate the failure processes，failure characteristics and ultimate capacity.It was shown that, due to the knocking out of the slot rib, the upper and lower core columns were connected and thus made them collaborate.As a result, the shear strength of the grouted slotted block masonry was moderately higher than that of the ordinary grouted masonry.Based on the shear mechanism of concrete block masonry, a shear strength formula of grouted slotted block masonry was built with Hoffman criteria, and a uniform shear strength formula suitable for both slotted and unslotted block masonry was proposed.The calculated values, which were generated by formula developed in this method, were in good agreement with the test results.