In this paper, the tuning of walk-off length and the optimal period of periodical-inverted GaAs crystal in narrow-band terahertz-wave generation by difference frequency mixing was numerical simulated and analyzed in the condition of different wavelengths and durations of pump pulse.The influence of the number of domains of periodically-inverted GaAs crystal on the THz-wave spectrum was also studied.The temperature tuning properties in periodical-inverted GaAs crystal were calculated and analyzed with the temperature dependent Sellmeier function of GaAs crystal; the influence of temperature tuning on the THz-wave spectrum was also studied.The simulation showed a new way to generate the wide-tunable narrow-band THz wave with temperature tuning.These theoretical calculations served for the subsequent experiment as theoretical basis and reference.