The dynamic minimum thickness of cut for the ultra-precision machining surface quality is important influence. Between tool and the workpiece for the friction coefficient were analysised, the relationship of the friction coefficient and the MTC were discussed, and the MTC and its effects on surface roughness were a theoretical analysised and experimental verification with processed single crystal copper and single crystal aluminum by AFM’s diamond tip. The results show: the MTC of single-crystal copper (single crystal aluminum) is 5.2nm (8.2nm) in stable cutting conditions. Further processing single crystal copper (ingle crystal aluminum) with cutting thickness of 5.2nm (8.2nm), and the surface roughness Ra160nm (Ra110nm) is obtained. So the MTC is evolving with the friction coefficient and the force ratio, theoretical MTC tends to be minimal value then before the adhering effect to reach remarkable. Appropriate adjustments cutting parameters, the cutting process can always micro-cutting phase to reach the steady-thin chip, and no plowing phenomenon. So the surface residues highly were reduced and higher surface quality was achieved.