The invention relates to a novel dyeing process of a polyester / cotton knitted fabric. The process is characterized by comprising the following steps: pre-treatment / washing in a single bath; pickling and neutralizing; deoxygenating; cotton dyeing; water washing; acid passing; TCW cleaning; hot washing; water washing; and color fixing. Compared with a conventional process, a single bath agent Yakesai TCB-N is adopted to combine pre-treatment and dyeing, so that the oxygen bleaching and dyeing in the single bath can be realized technically; after washing, no cleaning is performed, and meanwhile, the hot washing numbers of time and two times of reductive cleaning are reduced, and cotton dyeing is directly performed, so that the process is shortened; after cotton dyeing, a TCW environmental cleaning process is adopted to replace a conventional two-time soaping step at 95 DEG C, and meanwhile, the hot washing numbers of time is reduced, so that the process is relatively environment-friendly, COD is low, the sewage treatment burden is alleviated, the benefit is increased, the pollution discharge is reduced, and an effect of saving energy and reducing emission is achieved.