The invention relates to a method to simply and efficiently prepare a 2-alkyl substituted chromanone compound and relates to the field of medicine, organic chemical industry and fine chemical industry. The method uses chromone compounds and fatty aldehyde compounds as materials, and the 2-alkyl substituted chromanone compound is synthesized in the presence of the free radical initiators. The reaction conditions include: heating to 100-150 DEG C for 10-15 hours; isopropanol, tertiary butanol, chlorobenzene, acetonitrile, dimethyl sulfoxide and acetone are used as reaction solvents; tert-butyl hydroperoxide, tert-butyl peroxybenzoate, hydrogen peroxide, dicumyl peroxide and benzoyl peroxide are used as free radical initiators. Simple post-treatment can be performed after the reaction so as to obtain a series of 2-primary, secondary or tertiary alkyl substituted chromanone compounds.