The invention discloses a horizontal-type solid fermentation tank and fermentation method for Pu-erh tea. The fermentation tank comprises a tank body supported by a tank body support, and a clamp jacket is installed outside the tank body; the top of the tank body is provided with feed inlets, exhaust ports, diversion plates connected with heating wires, a water inlet and a water replenishing and inoculation opening; the bottom of the tank body is provided with a discharge outlet, a water vapor inlet, a sterile air inlet, a carbon dioxide inlet, a drying ventilation opening and a water outlet, and a stirring system is further arranged in the tank body. According to the fermentation method, a traditional Pu-erh tea pile-fermentation technology is changed, production standardization and specification rationalization of the Pu-erh tea are achieved on the condition that fermentation conditions such as microorganism species, tidal prism, temperature, fermentation time, inoculated-pathogen quantities and oxygen and carbon dioxide content of the Pu-erh tea are comprehensively considered, the fermentation process of the Pu-erh tea is artificially controllable, and the quality of the Pu-erh tea is more stable, safer and more controllable.