Abstract: This paper is a preliminary study of strength characteristics of sand-gravel with different contents of fine particles （minus 0.lmm）, based upon the data obtained from large scale direct shear test. Some Conclusions in this paper are, （ 1 ）The Mohr's envelope is a curve passing through the origin and good enough to be expressed by exponential equation τ=Ap（σ/p） ; （ 2 ）The effects of fine particles contents on thestrength of Sand-gravel with different contents of coarse aggregates have diffreent characteristics and magnitude; （ 3 ）The effects of fine particles in different nature on the strength of sand-gravel even with same contents of coarse aggregates also have different magnitude; and （4）Graphs of shear displacement against time show that the starting point of straight line section is a characteristics point worth noticed.