The invention relates to a fluorescent whitening agent, in particular to a fluorescent whitening agent composition for cotton cloth, which comprises the components by mass percent: 20-80% of fluorescent whitening agent BA, 0.0-1.5% of disperse violet 2RL, 0.0-1.0% of disperse brilliant blue E-4R and the balance of anhydrous sodium sulphate, wherein the fluorescent whitening agent BA has the following structure. The fluorescent whitening agent greatly improves the whiteness value of the cotton cloth, and the whiteness value can be improved to be more than 16; and under the condition of leading the cotton cloth to reach the same whiteness requirement, the dosage of the fluorescent whitening agent is reduced, so that the cost is saved.