The invention discloses a stainless-steel kitchen-garbage-treatment all-in-one machine. The stainless-steel kitchen-garbage-treatment all-in-one machine is composed of a mixing treatment device, a feeding device, a marsh gas collecting device and a marsh gas purifying device. The mixing treatment device comprises a feeding hopper, a smashing cavity and an arc-shaped outer shell. The feeding hopperis located over the smashing cavity, the smashing cavity is located over the arc-shaped outer shell, a circular-arc-shaped inner wall is arranged inside the arc-shaped outer shell, a storage cavity is formed between the arc-shaped outer shell and the circular-arc-shaped inner wall, a fermentation cavity is enclosed by the interior of the circular-arc-shaped inner wall, a liquid storage cavity isformed in the two sides of the fermentation cavity, a liquid recycling cavity is formed under the liquid storage cavity, and a solid recycling cavity is formed under the fermentation cavity. The kitchen-garbage-treatment all-in-one machine is simple in overall structure and high in integration degree, kitchen garbage can be subjected to treatment such as smashing, solid-liquid separation, oil-water separation, fermentation and marsh gas recycling, and the use ratio of materials is increased; the overall processing and treatment cost is low, and high application and popularization value is achieved.