In order to study the effect of fine particle content on the shear behavior of medium fine sand, different proportions of fine-grained soil were added to the standard medium-fine sand, five kinds of mixed fraction samples with different fine content were prepared and the direct shear tests were carried out, the effects of different fine contents and normal stresses on shear behavior were studied, and the motions of micro particles were also analyzed. The results show that, the samples with different fine contents show softening phenomenons to some certain extent under lower normal stresses, the samples with fine content of 0%, 10% and 20% show hardening under 200kPa normal stress; the peak strength of different samples and the corresponding horizontal strains, and shear stress under the same strain increase with the increase of normal stress; the friction coefficient of the samples decrease with the increase of the normal stress when the normal stress doesn’t exceed 100kPa, and then the rangeability is not large, the volumes of samples first appeare shear shrinkage and then gradually changed to shear expansion, and the normal stress threshold of the rangeability was 100kPa; The varies of shear strength of samples with the change of fine content under different normal stresses are different, however, 5% and 20% of fine contents usually correspond to the extremums of curves of the intensity change. The shear behaviors of medium fine sand with different fine content are obviously different, which provides a theoretical reference for practical application and related research.