To control synthesis of carbon encapsulating metal nano-particles, the reations were carried out at 400 ℃ and using iron supported on sodium chloride as catalyst which contain about 0.3, 1.6, 3.3 and 5.2 wt% of iron. The samples were examined by scanning electron microscopy and high resolution transmission electron microscopy. The results show that carbon encapsulating Fe cores nano-particles with diameters in the range 20-50 nm and the mean diameter 30 nm were obtained using the catalyst containing 0.3wt% iron. When using the catalyst containing iron of 1.6 wt%, the product with diameters in the range 35-60 nm and the mean diameter 49 nm was obtained. While using the catalyst containing iron of 3.3 and 5.2wt%, there was no obvious difference in diameter of the two products, and the product with diameters in the range 40-100 nm and the mean diameter 65 nm was obtained.