Microstructure dependent on silicon and formation of 1：13 phase in LaFe13-ySiyC0.2 compounds was investigated. C and Si elements played different roles in assisting the formation of 1：13 phase. Si could inhibit the growth of α-Fe. The volume fraction of La-rich phase increased with the increase of Si content in the LaFe13-ySiyC0.2 ingots. When Si content was lower in LaFe13-ySiyC0.2 （S≤1.0）, α-Fe was excess and grew very large in the initial annealing process. As a result, a large amount of α-Fe remained even after a long time annealing process. Carbon doping could accelerate the formation of 1：13 phase in the LaFe13-ySiyC0.2 compounds. The amount of the 1：13 phase reached -90 vol.% in LaFex3_ySiyC02 （y〉1.2） after annealing at 1353 K for only 3 d. After optimized annealing, large magnetic entropy changes were obtained in LaFe13-SiyC0.2 compounds （18.6 and 15 J/（kg.K） in 0-2 T field change fory=1.2, 1.4, respectively）.
