The invention discloses a preparation method of doxorubicin hydrochloride magnetic nanoparticles. The preparation method comprises the following steps: (1) dissolving nano block polymer polyethylene glycol-polylactic acid in dimethyl formamide to prepare a solution A; (2) dissolving doxorubicin hydrochloride in dimethyl formamide to prepare a solution B; (3) adding triethylamine into the solution B, and performing the deionization ultrasonic dissolving on the doxorubicin hydrochloride; (4) dissolving ferroferric oxide powder in tetrahydrofuran, and ultrasonically dispersing to obtain a solution C; (5) dropwise adding the deionized solution B into the solution A under a stirring condition; (6) stirring and uniformly mixing the doxorubicin hydrochloride and nano blocks, and volatilizing organic solvent to obtain medicine carrying micelle; (7) dropwise adding the solution C into the medicine carrying nano micelle obtained in the step (6), and uniformly stirring; (8) dialyzing to obtain magnetic medicine carrying nano micelle; and (9) adding a freeze drying protective agent into the nano micelle to obtain the magnetic medicine carrying nanoparticles. The method is simple in operation procedures and easy in operation.