To provide basis for the identification of disaster premonition, the deformation and stress-strain behaviors of highway slope is analyzed to determine the critical displacement thresholds and deformation evolution regularity at measuring points at ground surface. A strongly-weathered argillaceous siltstone slope of highway is taken as research object. A comprehensive safety monitoring system of corresponding early warning criterion is established based on the relation between deformation and safety degree together with in-situ safety monitoring and slope appearance. Moreover, to reveal the intrinsic relation among parameters and their contributions to the stability of slope, the relationships of cohesion, internal friction angle, unit weight, slope gradient against stability are analyzed through uniform design test in consideration of the main effects of factors and the interaction among factors; the changing of strength parameters and slip surface are examined, and the influences of excavation pattern and excavation level are analyzed as well. Results demonstrate that the quadratic polynomial function between stability coefficient F and parameters can be fairly well fitted through nonlinear regression analysis. The influence of materials is greater than that of geometric factors, while the excavation pattern and level is of small effect. Slip surface changes in a negative relation with the changes of cohesion and internal friction angle. The slope experienced three stages of displacement before instability.