In order to understand the various factors and influence laws affecting the shear strength index of red bed residual Deluvial soil fill, taking the red bed residual Deluvial soil fill in Chang Zhu Tan area as a representative, a large number of tests were carried out with a new compaction cylinder, and the influence laws of moisture conten, gravel content and compaction state on the shear strength index of test samples were deeply studied. The results show that with the increase of moisture conten, the overall shear strength index of filling decreases significantly, and the weakening effect of moisture conten on C value is much greater than that of φ Value; The gravel in the fill can effectively improve the overall shear strength of the fill. When the gravel content is about 10%, the C value of the fill is not weakened or slightly weakened, the φ value can be greatly increased, and the optimization effect may be reduced if the gravel content is too high or too low; The shear strength index of fill has a positive correlation with the compaction coefficient, and the cohesion c value is more sensitive to the change of compaction coefficient; After the compaction coefficient reaches 0.90, the shear strength index of the filling slows down with the increase of the compaction coefficient. Combined with the calculation results of the self stable slope angle of the filling slope, it is concluded that the engineering cost performance is relatively high when the compaction coefficient is 0.90.