on 表示关于的时候,一般指学术性的
如:The teacher told us a story about Lei Feng. It's very moving.
He will give us a talk on the history of the Party.
他将给我们做个关于党史的报告
再如: We're going to listen to a lecture on African history this afternoon.
今天下午我们将听一个关于非洲历史的演讲。
about 常用于简单的或浅显的论述等,是一般用语,多用于讲故事,谈话;思考等;
如:What are they talking about?
他们在谈论什么?