  Knowledge graphs (KGs) have been widely used for question answering (QA)
applications, especially the entity based QA. However, searching an-swers from
an entire large-scale knowledge graph is very time-consuming and it is hard to
meet the speed need of real online QA systems. In this pa-per, we design a
sub-graph searching mechanism to solve this problem by creating sub-graph
index, and each answer generation step is restricted in the sub-graph level. We
use this mechanism into a real online QA chat system, and it can bring obvious
improvement on question coverage by well answer-ing entity based questions, and
it can be with a very high speed, which en-sures the user experience of online
QA.
