camera panasonic aj-px270 problem -there is so much noise on object in it

We need a clip to look at. Noise suggests something adrift with your camera settings. Too little light, added gain, poor white balance, strange menu settings and poor exposure. Your camera should be pretty good, so we need a picture and more details.

I’m a tad confused – I pulled your clip into premiere and thought it looked pretty good, so tried a key and here’s the still from it. I didn’t play too much with the edges. I’m not seeing the noise you are describing and the key works pretty good. Have I missed something?
EDIT – I did the test with a still and never bothered playing it and that’s when it suddenly hit me – the frame to frame differences are pretty huge. Missed on the still. I’ve not seen this before and I don’t see what makes the frame to frame differences so big. I’ll have a think but something weird in the encoder – possibly even a real fault.It looks like the lighting is ok, the focus sharp but something causing that shift. Sorry for not thinking to make the video roll!

No, the usual camera adjustments aren’t specifically needed for green screen, and after all, your noise is not in the background, it’s on the solid colours – brown jacket worst of all. It’s the differences between the frames that points to random noise – different positions in the frame each frame? Have you already done any tweaking and maybe squashed the blacks, or then pulled them a bit in another – that kind off thing? You could also try a few experiments. Shoot solid colour full frames of different hues and intensities and see if the problem is in one of the colour channels – so maybe you will track it down to say, noise in the blue channel when the intensity is low? If this is the case, you can then experiment to see if adjustments cure it, or a factory reset – but the illumination level in that clip looks bright enough to make gain an unlikely cause, so it could, once you track down where it is worst, be a real fault. Random noise is one thing, but noise is usually consistent and not random like this. If one frame is noisy, then the next is too.

For green screen, the edges are usually the issue, and the colour system needs to be able to handle green accurately. Coding issues often make some formats less good – but green screen isn’t really your problem, because the green channel appears to key quite well.