The invention relates to a sustained-release microsphere injection containing an antitumor drug (2-methoxyestradiol), and the sustained-release microsphere injection can be used for effectively solving the problems that a conventional drug delivery system for 2-methoxyestradiol is not ideal in tumor treatment effect and has side effects. The technical scheme adopted for solving the problems is as follows: the sustained-release microsphere injection consists of the following parts by weight percent: 5-50% of sustained-release microspheres and 50-95% of solvent system, or independent sustained-release microsphere. The sustained-release microsphere injection can be used for realizing the purpose that the effect of drug can be sustained for a long time by one-time drug delivery, and overcoming the defects and shortcomings of a conventional 2-methoxyestradiol delivery system; and according to the sustained-release microsphere injection, the effective blood concentration can be maintained in the body for a long time, the dosage amount is only 1/30 that of the conventional drug delivery, the tumor inhibiting efficiency is 62% and is higher than that of the intravenous injection drug delivery by about 45%. The sustained-release microsphere injection can be used for reducing the dosage of the drug (toxic and side effects) and has the obvious advantages of improving the drug therapeutic effect.