The invention discloses a biogas digester, comprising a feeding chamber, a fermenting chamber, a secondary fermenting chamber and a discharging chamber; one side of the fermenting chamber is provided with the feeding chamber, the other side of the fermenting chamber is provided with the secondary fermenting chamber, one side of the secondary fermenting chamber far away from the fermenting chamber is provided with the discharging chamber, wherein the top of the feeding chamber is provided with a feeding port, the top of the feeding port is provided with a cover plate, a seal door is arranged below the cover plate I, the bottom of the inner wall of the feeding chamber is provided with an inlet that is close to the fermenting chamber, and an inlet pipeline is connected to the bottom of the inlet. The biogas digester has the advantages, for instance, energy can be saved, the environment can be improved and protected, chemical fertilizer and pesticides can be saved, crop yield and quality can be increased, and the development of the breeding industry can be promoted.