The invention relates to a black tea fermentation machine which comprises a fermentation box, wherein a screen frame is arranged in the fermentation box; at least one fermentation screen is arranged on the screen frame; a hot moisture device used for regulating the humidity, a hot air device used for regulating the temperature, and a control device used for controlling the operation of the fermentation machine are assembled in the fermentation box; and the control device is respectively connected with the hot moisture device and the hot air device. Heat is transmitted into the fermentation box through the hot air device, so that the temperature in the fermentation box is guaranteed; moreover, water is heated through an electric heating tube of the hot moisture device, so that the water is evaporated, and the temperature in the fermentation box is guaranteed; and therefore, the fermentation temperature and humidity can be met at each position on the screen frame, and tea leaves arranged on the screen frame are uniformly fermented, so that the color, aroma and taste of black tea are guaranteed, and the fermentation quality of the black tea is improved.