In the growth process of heavily arsenic-doped Czochralski silicon crystal, the arsenic dopant has its strong evaporation. To suppress the influence of As evaporation on the resistivity of silicon crystal, the evaporation rate constant of As should be determined. The curve of As concentration in a crystal sample versus evaporation time is given in a measurement experiment. Then, through the linear regression analysis of the experimental curve, the As evaporation rate constant in the growth process of the heavily As-doped silicon crystal (1.43×10-4 cm/s) is obtained. The result is verified to be correct and effective in the practical applications. This is of great significance to the precise control of the resistivity of heavily As-doped silicon crystal.