The pulse duration is a critical parameter of picosecond-petawatt laser systems because it directly affects the results of high-energy-density physics experiments. This study systematically investigated the effects of the spectral width, central wavelength, and beam-pointing deviations on pulse duration stability at the SG-II facility. A theoretical analysis of the relationship between spectra and pulse duration is conducted to quantify the impact on pulse duration stability, and the results are further validated through experimental measurements. Additionally, beam-pointing deviations at the stretcher significantly affect the pulse duration. For example, a 27 µrad deviation can induce a 30% pulse duration variation. In contrast, the compressor exhibits greater robustness. Based on simulation and experimental results, we identify operational tolerance ranges for spectral width and beam-pointing deviation to maintain pulse duration stability within 5% at the SG-II facility. These findings provide critical guidance for optimizing the performance and reliability of CPA/OPCPA-based high-power laser systems.