The present invention provides a nanocarbon-iron composite system which is a composite structure formed by interaction of acid-treated nanocarbon serving as a carrier, with and ferrous ions and/or ferric ions in an iron salt. In an in-vitro experiment and an animal experiment, the nanocarbon-iron composite system of the present invention shows a very efficient inhibition effect on solid tumors containing liver cancer, breast cancer and cervical cancer and has an excellent targeting property. Accordingly, the present invention further provides a preparation method of the nanocarbon-iron composite system, use of the nanocarbon-iron composite system in preparation of a drug for treating solid tumors, and a suspension for injection based on the nanocarbon-iron composite system.