can bipolar surround speaker on backwall with 5.1

You can't mount a speaker which radiates both forward and backward on a wall; the back radiation would have nowhere to go and cancel out the forward radiation. In any case you would get no benefit from using bipolar radiators in regard to sound distribution when mounted in this manner. I have heard of them being mounted between rooms so they could radiate equally into each but these were full range speakers.

I don't think they will make most video people happy that way.If they were more like the S5,you might be able to pull it off.If you are right against the back wall,then it may get by.If the wall is extremely wide,it may get you in the field, but I doubt it.Others mat disagree.Link for them.[http://www.psbspeakers.com/products/Imagine/Imagine-S-Surround#product_detail][http://www.psbspeakers.com/products/Image-Series/Image-S5-Surround]

My living room is 19 *12, and the back wall is at 12 side. In that case, is anyway to get a surround evelopement in my case? If bi-pole or di-pole will cancel their backward/forward with my original idea, would a pair of direct radiate speakers work?

Yes, but get ones intended for wall placement. Most intended for HT use should work. Most two channel speakers are designed to be used out into the room and the sound is affected if placed too close to wall. You are going to have trouble with the window side of your room, will be very reflective. Have you consideded an omni speaker like the Shanian Compass? Not 5.1 but would give you a large non directional sound that might work well in your room.