Uncertainty reasoning is one of the important directions in the research field of artificial intelligence and plays a key role in rules extraction in decision making with uncertainty information.This paper utilized the lattice-valued concept lattice to depict uncertainty information and gave the external approximate uncertainty reasoning method.Concretely,from the set including degree,the relations between the intent set and the extent set are analyzed and the external approximate uncertainty reasoning methods are given.The properties of monotony,quasi-monotony,consistency and coherency about this uncertainty reasoning are respectively validated.Furthermore,the relationships of the external approximate uncertainty reasoning which was synchronously operated on the lattice-valued formal concepts are talked about.