Abstract： Objective To establish the femtosecond laser experimental platform in vitro for numerical controlled cavity preparation,and to evaluate the roughness quantitatively and observe the microscopic morphology of the cutting surface.Methods Enamel and dentin planes were prepared on human third molars.A universal motion controller was used to control the samples to do rectangle wave motion perpendicular to the incident direction of the laser at focus. The surface roughness was obeerved with confocal laser scanning microscope.Results Precise ablation of the dental hard tissues can be achieved with the established femtosecond laser numerical control platform. For enamel,the surface roughness of the cavity inside laser scanning line was 7.173 μm at the bottom and 2.675 μm on the wall of the cavity.The surface roughness of the cavity between laser scanning lines was 13.667 pm at the bottom and 33.927 μm on the wall.For dentin,the surface roughness of the cavity bottom was 51.182 pm and 25.629 μm for the wall.Scanning electron microscope images showed no micro-cracks or carbonization on enamel,while carbonization,cracks and a small amount of crystalline particles were observed on dentin.Conclusions Precise tooth preparation can be achieved with femtosecond laser numerical control flatform.The surface roughness of cavity wall was less than that of the bottom and can meet the clinical needs.Suitable femtosecond laser output power should be set for different cutting objects,otherwise it may result in tissue damages.