The invention relates to the field of metal material heat treatment, in particular to a high-temperature quenching-deep-undercooling-low-temperature distribution heat treatment method for metastable state austenitic stainless steel and stainless steel. The high-temperature quenching-deep-undercooling-low-temperature distribution heat treatment method for the metastable state austenitic stainless steel is characterized in that a metastable state austenitic stainless steel hot-rolled plate is subjected to complete austenitizing, and then rapid cooling is conducted to the room temperature; then,deep undercooling treatment is conducted, the metastable state austenitic stainless steel hot-rolled plate generates a large amount of martensite at the ultralow temperature, and then temperature riseis conducted to the room temperature; finally, the metastable state austenitic stainless steel hot-rolled plate is heated to 350-500 DEG C, heat preservation is conducted for 1-30 min, the element Cand the element N are distributed to the austenite from the oversaturation martensite, the content of the austenite is increased, and stability of the austenite is improved. Through the heat treatmenttechnology, different phase changes are controlled, and a martensite, austenite and trace carbonitride complex phase structure at the room temperature is finally obtained, wherein the toughness of materials is improved through the austenite, and the strength is improved through the martensite. Compared with an existing metastable state austenitic stainless steel treatment technology, the technology is simple, cost is low, and the treated metastable state austenitic stainless steel has the ultra-high toughness performance.