As a concept proposed to mitigate the global warming,carbon neutrality mainly refers to the net CO_2 emission into the atmosphere to be zero inside a certain spatial and temporal boundary. In recent years,negative carbon has been even possible with the rapid development of renewable sources and carbon capture technologies. Thus,the framework of carbon neutrality requires a significant adjustment to embody such new technological elements. We reviewed the existing definitions and elements of carbon neutrality and discussed spatial and temporal boundary scales,then summarized three kinds of carbon neutral definitions: text,formulas and graphics. In particular,the proposed carbon neutral framework of the carbon capture system provided a quantization method for environmentally-friendly design of the carbon capture system,which could be applied for engineering design or assessment.