The invention relates to a method for preparing a selenide ferrous iron nanometer flower. The material can be used as an active material of an anode of a lithium ion battery. The method for preparing the selenide ferrous iron nanometer flower comprises the following steps that: according to the ratio of 0.1 mol:0.1 mol:100 mL, selenium powder, sodium sulfite and deionized water are picked up, heated and stirred to obtain a solution of Na2SeSO3; 2) according to the ratio of 10g:100 mL, polyvinyl alcohol and distilled water are picked up, heated and stirred to obtain a water solution of polyvinyl alcohol; 3) according to the ratio of 2.5 mmol:5 mL:20 to 30 mL : 20 to 30 mL, F3C2O4, citric acid with the concentration of 1 M, the solution of Na2SeSO3 and the water solution of polyvinyl alcoholare picked up, mixed and stirred, and by adjusting the pH value of the system to be 8-10, an even rheological phase matter is obtained; 4) the obtained matter is kept at a temperature of between 160and 180 for 10 to 24 hours and then naturally cooled to obtain a hydrothermal product; 5) the hydrothermal product is subjected to centrifugal separation; and 6) the hydrothermal product is dried to obtain the red brown selenide ferrous iron nanometer flower. The method has the characteristics of simple process and low synthetic temperature.