The paper presents a numerical method of the diffusion process whereas duration and temperature conditions of the diffusion could be set finetuned in advance. Impurity atoms of sulfur and the transition element manganese in single-crystal silicon were selected as objects of study. Sulfur and manganese were supposed to be diffused into single crystalline silicon in sequence while the diffusion temperature of sulfur was chosen to be 1250 °C and of manganese 1200 °C, respectively. Diffusion was numerically calculated for intervals 10 minute, 30 minute, 1 hour, 3 hours, 5 hours, 10 hours, 15 hours and 20 hours for sulfur. For all cases, the duration of diffusion of manganese diffusion was chosen as 30 minutes. Based on the numerical calculation results, it can be assumed that for depths up to 140 μm at a diffusion temperature of 1250 °C for sulfur, the optimal diffusion duration to ensure that concentrations of impurity atoms of sulfur and manganese would equal to each other, was revealed to be 5 hours.