In order to optimize the H+NCl3+HI chemical laser system, a Matlab code for chemical kinetics simulations was developed and the process of 生NCl(a1Δ)-I energy transfer chemical laser of the system was simulated using a one-dimensional premixed model. The influences of H, NCl3 and HI initial number densities and their ratios on small signal gain at different temperatures are examined. The optimum NCl3/H and HI/H ratios are determined by scanning computations when the temperature and H number density are fixed. Finally, the influence of H, NCl3 and HI ratios on maximum small signal gain coefficients and gain durations are discussed. It is shown that when temperature is assumed 400 K, initial H number densities are assumed 1×1015 cm-3, 1×1016 cm-3, 1×1017 cm-3, the maximum small signal gain coefficients can reach 2.6×10-4 cm-1, 2.6×10-3 cm-1 and 2.6×10-2 cm-1 respectively. The optimum NCl3/H and HI/H ratios to achieve maximum small signal gain are 45% and 11%, respectively. It is also shown that the optimum NCl3/H and HI/H ratios increase with the temperature, as well as the maximum small signal gain coefficients.