NOVELTY - Water-soluble iron salt composite nanoparticle comprises zinc cobalt iron oxide (Zn(0.4)Co(0.6)) as a core and zinc manganese iron oxide (Zn(0.4)Mn(0.6)) as a shell. The shell surface is modified with polyethylene glycol and doxorubicin hydrochloride nanoparticles. The nanoparticle is cubic in shape.    USE - The water-soluble iron salt composite nanoparticle is useful for treating nausea tumor diseases (claimed).    ADVANTAGE - The method is simple, economical and does not cause pollution to the environment.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for preparing composite nanoparticle, comprising: (i) adding iron acetylacetonate, zinc acetylacetone, cobalt acetylacetonate and 1,2-hexadecanediol into oleic acid, oleylamine and benzyl ether, heating to 180-210 degrees C for 1.5-3 hours, then raising temperature to 280-320 degrees C for 0.5-1.5 hours to synthesize nano-seeds, then carrying out centrifugal washing and drying; (ii) adding the nano-seed, iron acetylacetonate, zinc acetylacetone, manganese acetylacetonate and 1,2-hexadecanediol into oleic acid, oleylamine and benzyl ether, heating to 180-210 degrees C for 1.5-3 hours, then raising temperature to 280-320 degrees C for 0.3-0.6 hours to synthesize zinc cobalt iron oxide-zinc manganese iron oxide nano-particles, then carrying out centrifugal washing and storing in n-hexane; (iii) adding polyethylene glycol, 6-maleimidocaproic acid N-succinimidyl ester and 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride into pyridine, reacting for 0.5-1.5 hours, then adding 3-(3,4-dihydroxyphenyl)propanohydrazide and reacting for 7-9 hours, adding the resultant nano-particles, reacting for 11-13 hours, carrying out centrifugal washing to obtain 3-(3,4-dihydroxyphenyl)propanohydrazide-modified ferrite nanoparticles, which is stored in water; and (iv) adding doxorubicin hydrochloride aqueous solution into resultant nanoparticles, mixing ultrasonically, reacting at 28-33 degrees C for 45-50 hours, dialyzing and freeze-drying.