Under-sampling is an advantageous way for lowering sampling circuit complexity in phase laser ranging while maintaining high modulated frequency operation. Improving the accuracy of the ranging system is the aim of the proposed selection criteria with involved under-sampling parameters. These parameters include signal frequency, sampling frequency, and calculation points. Setting the number of one periodic sampling points to be an integer power of 2 (p o w e r=2-6) optimizes the accuracy in integral periodic sampling. Levering up calculated periods with limited calculated points and averaging the calculated phase by employing the corresponding average parameter can both enhance accuracy in non-integral periodic sampling. These criteria are verified through derivation and simulation and are applied to the ranging system. The experimental results demonstrate that, by applying these selection criteria, the phase detection accuracy in the under-sampling ranging system can be potently improved without any pre-processing or algorithmic refinement.