To improve the measurement and evaluation methods of a machined micro/nano scale V-shaped groove, a single-point diamond turning was employed to machine the V-shaped groove of optic glass in micro/nano scale, and a non-contact laser measuring technology was used to analyze the topography of machined V-shaped groove. The micro/nano scale cutting of the V-shaped groove of optic glass was conducted by using the sharp cutting edge of a single crystal diamond. Then, the machined V-shaped groove was measured by a 3D laser meter to compare its profile,and the evaluation mode of the shape error PV and tip arc-radius of the V-shaped groove was established. Finally, the form principle of cutting depth and the angle of V-shaped groove were analyzed and the effect of sub-micro scale cutting depth on the shape error PV and the tip arc-radius was investigated. The results show that there exists a critical cutting depth of 0.386 μm,when cutting mode is transferred from a brittle cutting to a ductile cutting in sub-micron-scale space. In ductile mode cutting with a cutting depth less than 0.386 μm, the diamond tool tip can be replicated to the workpiece surface and to produce a sub-micro-scale V-shaped groove with a cutting depth less than 0.386 μm and a shape error PV about 0.103 μm. In addition, the tip arc-radius of V-shaped groove decreases in ductile mode cutting when the cutting depth is decreased, so to get a V-shaped groove with the tip arc-radius of 0.182 μm,the cutting depth should be controlled below the critical V-form cutting depth of 0.365 μm. These results also show that the parameterized model of shape error PV and tip arc-radius can be established by using 3D data derived from non-contact laser measurement, and can be employed to evaluate the machining precision of micro-scale V-shaped grooves.