Unreasonable utilization of stalk resources leads to environmental pollution and resource waste in rural areas. Stalk returning is one of the promising technologies to improve the physical and chemical properties of soil, soil fertility, and soil organic matter. Corn stalk could be transformed into biochar and return to the field in-situ by pyrolysis and carbonization returning technology. There are some researches on mobile pyrolysis equipment, however, the complex structure of the equipment makes it hard to realize carbonization and returning to field in-situ. Therefore, a mobile pyrolysis and carbonization returning to the field in-situ integrated equipment was developed. A self-heating reaction system was established based on the principle of stalk internal thermal low oxygen carbonization. Meanwhile, the key parts were designed such as pyrolysis and carbonization reactor, and pyrolysis gas clean combustion chamber. The equipment integrated multiple technologies and devices. Such as stalk collection and crushing and transportation mechanism, flue gas recycling, torrifacation, and biochar in situ returning technology. The power system was equipped as well. The results showed that the material handling capacity of the equipment was 50kg/h, the yield of biochar was 21%, and the conversion efficiency was 74.6%. Furthermore, the mass concentration of NOx and SO2 in flue gas were 184mg/m3 and 26mg/m3, respectively. In parallel, the mass concentration of particulate matter was 17.8mg/m3. The emission met the flue gas emission requirements. The physical and chemical properties (total carbon, fixed carbon) of biochar, metal elements content, and the amount of biochar returned to the field met the requirements of standard of grade I biochar in DB21/T 3314—2020. The equipment could realize lower carbon emission, self-heating, and field mobile operation, which was beneficial to the utilization of corn stalk. Moreover, it was of great significance for the promotion of stalk returning technology in-situ.