I bleed the oil furnace, it runs normal for a minute and then the pilot light die out. So far I have bleed about a 1ltr of oil from furnace. What do I need to do to keep the pilot light lit ?

If this is a standard oil furnace with a gun burner there is no pilot light. When the burner starts the flame starts at full volume. The flame is lit by a high voltage transformer.

Now with that said eventually if you bleed the line it should stay running UNLESS you have a air leak in the system.

Lines that are not tightened correctly,oil filter housing leaks,pump end shaft seal leaks, loose packing on valves and more can cause the burner suck air and fail to keep running. If it was as simple a situation as running out of oil with no other work done on the system it should relight after being bled a few times. If anything else was done to the system then I would look in that work area for the problem.

If you cannot get it going it might be a good time now to have your oil burner serviced before the cold weather sets in. Oil burners need to be serviced every year to maintain efficiency and save you $$$ on your oil bill.