If have a closed 2-D tube with a film in it, and want to set different pressure between the film(such like at one side is 1 bar another side is 5 bar). How to do this please?

You use the function Solve-initialize-patch.

First, initialise the whole domain with - say - 1 bar. Then, mark the region where you need 5 bars (using Adapt - region). You now have a register containing the limited cells. Use the patch dialog to patch the new pressure into the wanted marked region using the created register.