Turbulent combustion remains to be one of most complicated technologies due to the complexities of turbulence and combustion as well as the interaction of both. This paper presents a vitiated coflow combustor, which is newly used for the fundamental research into turbulent combustion. The characteristics of controllable active thermo-atmosphere (CATA) of a vitiated coflow combustor are investigated. The results show that the oxygen mole frac- tion of vitiated coflow flames between 0% and 21% yield coflow temperature between 700 and 1500 K, and there is a constant temperature space as a cylinder with a radius of 40 mm. These features of the vitiated coflow indicate the exis- tence of a controllable active thermo-atmosphere, which benefits the basic study on the autoignition of a combustible mixture in a homogeneous charge compression ignition (HCCI) combustion. Turbulent combustion remains to be one of most complicated technologies due to the complexities of turbulence and combustion as well as the interaction of both. This paper presents a vitiated coflow combustor, which is newly used for the fundamental research into turbulent combustion. The characteristics of controllable active results reported that the oxygen mole fraction of vitiated coflow flames between 0% and 21% yield coflow temperature between 700 and 1500 K, and there is a constant temperature space as a cylinder with a radius of 40 mm. These features of the vitiated coflow indicate the exis- tence of a controllable active thermo-atmosphere, which benefits the basic study on the autoignition of a combustible mixture in a homogeneous charge compression ignition (HCCI ) combustion.