Why is it when I export my iMovie it's bad?

Everytime I edit a video on iMovie 11' and export it the quality is ALWAYS band when I export it. I'm recording off a Nikon 1 J1 camera and that has great quality… Please Help

You did not tell us the settings when the video is captured in the J1 and you did not tell us the settings used when exporting from iMovie. Assuming the video is captured at highest quality, when I export from iMovie, at the command line, under "File", select Share, then File. On the right, there's a selection "Size". Select 1920x1080 or 1280x720 for high definition, lower compression, video.