Chaos computing is a new scheme which can construct fundamental logical gates by using one chaotic unit. In this paper, we propose a new method to implement full adder based on chaos computing. By setting different thresholds and judgment conditions, the full adder is implemented by using only one chaotic unit. This method reduces the complexness of the structure of full adders and provides certain flexibility compared with the traditional method. At last, the Logistic mapping is taken as an example to show how to implement a full adder by using one chaotic unit.