Using zircon, boric acid and carbon black as starting materials, ZrB2-ZrO2-SiC composite powder was synthesized by calcining at 1 500 ℃ in flowing argon atmosphere. The effects of the soaking time (3, 6 and 9 h) and the addition of additive AlF3 (0, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%, by mass) on the phase composition and the microstructure of the synthesized products were investigated. The results show that: (1) ZrB2-ZrO2-SiC composite powder can be synthesized by carbothermal reduction at 1 500 ℃ in flowing argon atmosphere; ZrB2 and ZrO2 are granular-like, and SiC crystals are fiberous; (2) with the soaking time increasing, the amount of ZrB2 increases, the amounts of m-ZrO2 and SiC decrease, and the total amount of nonoxides ZrB2, SiC and ZrC gradually increases; the optimal soaking time is 3 h; (3) compared with the sample without AlF3, the sample with 0.5% AlF3 has decreased m-ZrO2 amount, noticeably increased ZrB2 amount but decreased SiC amount; however, when the addition of AlF3 increases from 0.5% to 2.5%, the m-ZrO2 amount increases, the ZrB2 amount decreases, and the SiC amount changes slightly; the optimum AlF3 addition is 0.5%.