The present invention relates to an Agomelatine acid radical complex in formula (I) and the preparation method thereof (HX = H2SO4, RSO3H (R = CH3, Ph, 4-CH3Ph)). The solubility of the Agomelatine acid radical complex obtained by the method of the present invention is significantly improved compared with Agomelatine, has good stability and higher purity, and is suitable for application in finished-product medicinal preparations. The preparation process is quite simple, and a product with high purity can be obtained without special operations.(HX = H2SO4, RSO3H(R= CH3, Ph or 4-CH3Ph)).
