This paper probes into the influence of rock properties,clay powder content and the maximum particle size on MB value of the manufactured sand,and analyzes the influence of MB value on the fluidity,mechanical properties and pore structure of mortar.The experiment shows that MB value of the manufactured sand of sandstone linear increases with the clay powder content,and decreases logarithmically with the increase of the sand’s largest particle size.The fine powder particle is an important factor affecting the MB value,but the influence of the mineral lithology on MB value is insignificant.Fluidity and mechanical properties of mortar decrease with the increase of MB value,especially when the MB value is greater than 1.5. With the increase of MB value,porosity and average pore diameter increase,the quantity of harmful holes increases and that of the harmless hole such as gel hole reduces,which leads to degradation of the pore structure.It is recommended to control the MB value of manmade sand to no more than 1.5 in the process of site manufacturing.