The tailings sample has characteristics of easily to be disturbed in the process of both transportation and storage. However

limited by human resources as well as project budget

or else factors

it is impossible to establish field laboratory for all upstream tailings dam during their engineering geological exploration

thereby leading to errors between the shear strength index and practical situation. For this reason

an extensive field testing is carried out in a lead-zinc mine tailings dam

the water content and standard penetration number can be easily obtained from field testing; and the internal friction angles of tailings as it changes through standard penetration number under the influence of the water content are studied. Considering the effect of overburden pressure

a amended expressions of standard penetration number is proposed. And using the standard penetration number，a estimation method about the internal friction angle of tailings is deduced; Finally

several examples are given to verify that except for the situation when the amended standard penetration number is N1 >8（5%< <20%），this method can estimate the internal friction angle of tailings sand effectively. The results show that

the method has a high application value in upstream tailings dams’ engineering geological exploration in the future.