I have IMAX B3 PRO charger. And 2200 mah 3s battery. After some time connecting battery. .Two lights turn into green but one light remain red.i think battery is not balanced. I want to know how I can balance my lipo.

That means lipo not balanced.Try keeping it for more time till it turns green.Or sometimes the lipo may have a dead cell.

First check volts at every cell, if one cell is dead, try to charge it with any dc charger at 4.5 volt for only two minutes, and recheck volt and charge until it show above 3 volt, then charge with your balance charger..

I checked with multi meter. All cells are perfect. But when I charge batter one light remains red.  What to do.

What's the actual reading of each cell after the end of the charging session?

And how old is the LiPo?
Maybe one of the cells degraded by a bit due to regaulr usage or overdischarge?

Lipo is new just charge for three times. Reading is 3.85..7.8..and 11.9

Is this reading from after charging it completely?
If yes, i have bad news for you.

If not, let the LiPo stay attached to the charger for about 2 hours and then take fresh readings.

Here is the voltage of each cell of your LiPo based on the readings that you have provided:
Cell1: 3.85v
Cell2: 3.95v
Cell3: 4.10v

The voltage of each cell in a healthy battery should be 4.23volts

Seems you've let it discharge way beyond the nominal 3.7v per cell.
First off, watch this video to have a better understanding about LiPo's:
Second, Watch this video to understand how can a LiPo alarm save your LiPo's from the bin in the future:

Third, Get a LiPo Alarm before getting a new LiPo.  

BTW, in order to test the voltage of each cell using multimeter, check the voltage at the following pins on the balance lead:
Cell1: Pin 1 and 2
Cell2: Pin 2 and 3
Cell3: Pin 3 and 4

Thanks

Cell 1 is     3.84v
Cell 2        4.00v
Cell 3        3.99v

These reading are after use of 10 minutes.

 hello bhai..
 understanding lipo battery
 go to this link --

www.rchelicopterfun.com/rc-lipo-batteries.html

@kplkum ...after use of 10 mins
I would need the data for after charging the cell completely (for let's say 2 hours). Since based on that only one can confirm if the cells are damaged or fine.

The link provided by Rakesh_suthar will also help getting more information about LiPo's.

I charge my battery until two cells goes green but 3rd is still red. 3rd cell rating is 4.06 v . it do not reaching to 4.26v. What I do and what it's mean.

It means that 2 out of the 3 cells are good and the 3rd one is damaged and there is no way to recover it.
This 3rd cell will show great deal of voltage sagging.

Can I charge that single cell

Yes, you can. But the point is that since the damage has already been done, that cell will never reach 4.26 volts.
No matter what you try.
It's best to discard this Battery, and get a new Battery along with a LiPo Alarm so that you can avoid similar issue in future.