Just see as following image
what I want to realize is, when I choose a specific area in the Area dropbox, The Block dropbox only shows the content which only belong to the selected area. How to realize that in tableau? Area and Block are both parameters.
I would advice you to use filter. then for the block filter,click the arrow on the top right and select "Only Relevant Values".The block filter will then refresh after you choose an area to show only the blocks related to that area. For parameters currently the dynamic refresh feature is not present, though it is being demanded.