The invention discloses a dyeing agent for fabric dyeing. The dyeing agent is prepared from, by weight, 3-4 parts of yellow dyestuff, 3-4 parts of tea polyphenol, 10-13 parts of water, 1-3 parts of copper sulfate pentahydrate, 0.4-0.6 part of boric acid, 1-2 parts of propylene glycol, 1-3 parts of jack fruit shell powder, 0.5-1 part of ethyl acetate, 2-3 parts of assistant, 1-2 parts of defoamer, 3-6 parts of initiator, 1-3 parts of polyethyleneimine and 1-3 parts of light stabilizer. Dyed fabric has good color fastness, washing resistance, friction resistance and light fastness resistance all reach the level IV or above, the staining fastness can reach the level VI, The K / S value reaches 8.81 or above, environmental friendliness is achieved, and a certain healthcare function is achieved; the jack fruit shell powder is natural yellow and has the complementary effect with a tea polyphenol-copper yellowish-brown complex and the yellow dyestuff, the dyeing fastness can be greatly improved, and the color is fuller, more natural and softer.