Abstract: Sintering of roasting materials during calcination of vanadium slag may lead to low leaching ratio or even interruption of production processes. Reasons for material sintering and various influencing factors were studied. The research results show that the solid low melting point materials transform into liquid phase when the roasting temperature is higher than the melting point of the product,and larger diameter spherical sintered materials generate with revolving of rotary kiln. Roasting temperature and magnetic materials in the mixture are main factors for sintering. The length of firing zone is extended when the temperature is above 900℃,so low melting point materials have enough time to generate more liquid phase,result in sintering. With high magnetic material content in the mixture,temperature may be up to 1 000℃ locally due to superposition of the roasting temperature and the temperature rising during exothermic oxidation in the roasting process,and as a result the materials are severely sintered.