The invention provides a processing method of a big leaf 'post-fermented tea' dark green tea. The processing method is characterized by comprising the following steps: big leaf fresh leaf picking, water removing, rolling, drying, crude tea drying, classifying and bunching, sterilizing, inoculating, pile fermenting, turning and cooling, air drying and alcoholizing, vapor-pressing, airing, ageing, finished dark green tea; the inoculating refers to access eurotiaceae, and the eurotiaceae is the mixed thallus of aspergillus niger, rhizopus delemar, penicillium sp., aspergillus glaucus and brettanomyces intermedius; the mixed thallus is prepared from the following steps: every strain is subjected to liquid culture, is dispersed into hyphal bodies of 0.2-0.4 cm or so, suspended until 107-108 hyphal bodies or somatic cells are formed per milliliter with the volume ratio of 3: 1: 1: 8: 3, and mixed uniformly.