The invention discloses a tea bottle for fermentation of loose dark tea. The tea bottle comprises a bottle body (1) and a bottle cap (2), wherein the bottle cap (2) comprises a first bottle cap (21) and a second bottle cap (22), the first bottle cap (21) is buckled with an upper-end outlet of the bottle body (1), the second bottle cap (22) is arranged at the upper end of the first bottle cap (21), a breathable water absorption film layer (3) is arranged between the first bottle cap (21) and the second bottle cap (22), and ventilating holes (4) communicating with the breathable water absorption film layer (3) are further formed in the first bottle cap (21) and the second bottle cap (22). Air inside and outside the bottle can be replaced in the fermentation process of the loose dark tea, the oxygen supply for fermentation of the loose dark tea is guaranteed, the breathable water absorption film layer can preliminarily filter air entering the bottle from the outside and adsorb humid air accumulated at a bottle opening, and the conditions that water vapor is condensed and flows back to the bottle, the water content of the material at the bottle opening is too high and contamination of the bottle opening is caused by sundry bacteria are prevented.