Ultra precision machining of monocrystalline silicon to achieve damage-free surface is critical for the semiconductor and optical components. A profound comprehension of the material removal mechanism at the atomic scale is imperative for predicting and inhibiting defects during nanomachining, particularly within the ductile removal regime. This study delves into the deformation behavior and dislocations evolution in monocrystalline silicon, leveraging both ramp nanoscratching experiments and molecular dynamics simulations. The scratching force, friction coefficient and scratch morphologies were obtained in the ductile regime under different scratching velocities and normal loads. The rebounding of the scratched surface, attributed to the elastic deformation of the diamond structure Si and amorphous Si, was characterized by the variation of residual scratching depth and the nominal volume per atom. Furthermore, the transmission electron microscope observation was conducted to analyze the lattice defects including amorphous phase, dislocations and stacking faults in the scratching area. The subsurface exhibited a series of dislocation lines, situated distantly from the amorphous silicon layer, indicating the slipping of dislocations along priority orientations into the subsurface during ramp nanoscratching, which was consistent with the simulation results. Based on this, the dislocations evolution mechanism was elucidated at atomic scale through the analysis of dislocations propagation and the stress distribution. This work provides a theoretical guidance for the processing defects control during the ultra precision machining of monocrystalline silicon.