what is the difference between"about"and "on" when they are used for the meaning of "关于"

ON is used to suggest that a book, article, lecture etc is serious or academic, suitable for specialists.
ABOUT is usual when the information given is more general, or the style of communication is more casual.
A book ABOUT Asia is a book for the general public, whereas a book ON Asia is one for scholars.
Compare:
a book ON African history
a book for children ABOUT Africa and its people
a lecture on economics
a conversation about money
an article on British indutrial problems
an argument about strikes