Abstract: Nuclear data processing is an important interface connecting nuclear data and neutronics transport codes. The calculation of the unresolved resonance region is one of the key technical points of nuclear data processing. The resonance self-shielding effect in the unresolved resonance region with dense resonance distribution shall be considered in neutronics calculation. The probability table method is a common method to obtain the self-shielding cross section of the unresolved resonance region. The Ladder Sampling method is the most widely used probability table generation method at present. It constructs pseudo resonance sequences to be equivalent to the actual resonance structure to calculate the probability tables. The probability table calculation module based on Ladder Sampling method is developed in NECP-Atlas. The sensitivity analysis of complex error function calculation, chi-square random number generation, probability table partition, resonance formulas selection, sort algorithm and ladder number is carried out, and the optimal calculation conditions are determined to obtain the accurate probability tables efficiently.