Abstract: To meet the requirement of Nano-scale dimensional metrology, length standards with features below 100 nanometers were indispensible instruments. The length standards with periodic length of 213 0.1 nm were successfully fabricated through atom lithography, which was connected to atomic transition frequency and thus retraceable to a constant measured with highly accuracy. For further improvement of the quality of these standards, the evaluation and optimization of collimating the atomic beam were described in this article. A knife-edge was settled to cut the atomic beam collimated by the laser Doppler cooling. The fluorescence of the beam was collected to calculate its angular distribution and equilibrium transverse temperature. The stimulated absorption rate was considered and discussed. Full angular width at half maximum as small as 0.544 mrad was observed, corresponding to temperature of 343.8 K. Several angular distributions were measured by changing the laser characteristics to optimize the collimation.