Abstract: Some factors influencing silicon productivity were studied for producing polycrystalline silicon by zinc reduction.When the reaction reached equilibrium,the relation between gas phase compositions and temperature was analyzed at the Zn/SiCl₄ molar ratio of 2,4 and 8 under the pressure of 0.1,0.3 and 0.6MPa,respectively.The changes of silicon productivity with gas pressure,temperature and Zn/SiCl₄ molar ratio were discussed.The results show that lower temperatures,suitable pressures and higher Zn/SiCl₄ molar ratios have a positive effect on the zinc reduction process.The major side-reactions which affect the silicon productivity were then determined.Finally the optimum operating conditions for the zinc reduction process were presented as 1200K,0.2MPa and the Zn/SiCl₄ molar ratio of 4.Under the optimum operating conditions,the theoretical silicon productivity can be 90.3%.