byte array of image whether can make as the background of unity camera preview

Well, Texture.SetPixels takes an array of Color values. Is that what you mean? As for the background thing, you'd have to set up some kind of culling thing- have a second camera which renders first, with nothing in front of it except this image, and then have your main camera set its clear flags to 'none' so that it doesn't wipe the previous image. As for the preview thing, you can't really do that, but why do you want to?

I want to change the backgroud of the unity camera preview to the images that HTC mobile Camera captured,can you tell me how to do？

Like I said, have a second camera which only shows an image. If you have a Texture2D which you have parsed from the camera, just use that!