First of all, thanks a lot of answering my question. I become more clear about the idea.
I have just sat the geog exam, fortunately, they didn't ask the difference between the two.
However, it seems that the idea between TROUGH and COLD FRONT is still quite confusing as both are at the convergence of a warm moist air current with a dry cold current.
Besides, when I read my book, I saw the axis of the through connect with the cold front, which is originated from a temperate cyclone. it seems to make the case more confusing.