Have you met the similar question?

"Anyone using Flip Video and iMovie 09? I need help!I installed iLife 09, and just recently tried iMovie 09 for the first time. Pulled some videos off of my Flip and dragged them into iMovie. It looks like it imports them fine, but then in the preview panel it says "No Matching Video, choose a different option from the Show pop-up menu at the lower left corner". So I made sure that THAT menu says "All Clips" but still nothing is showing up." From Mac Rumors Forum

When quite a lot of these users are using Mac OS and need to edit flip videos in iMovie on their Mac system, however, flip videos cannot be directly imported to iMovie and to edit flip videos using iMovie, the key is will have to convert flip videos to iMovie supported formats.

The key to solve the question-convert flip videos to iMovie supported formats.Step 1: Add flip videos to the Mac Flip Converter Click the "Add File" button to add the flip videos you want to edit in iMovie to Doremisoft Flip ConverterStep 2: Select an iMovie format for your conversionClick the Profile drop-up list and select an iMovie format to convert your flip videos.Step 3: Convert flip video to iMovieClick the "Start" button on the lower right of the interface to start converting flip video to iMovie.

Then start to edit Flip video on iMovie:

1. Import the converted flip videos to iMovieSelect "Import Movies" from the File menu and now you can see the converted file appeared in the preview panel. Use the browser to select the converted flip videos.Step 2: Arrange video ordersDrag and drop the video files in the timeline to arrange them in the order you prefer.Step 3: Set start and endClick on the click icon to switch to the timeline view. Here you can trim your arranged clips for more precise editing. Simply use the Play head bar over the timeline and select your stop and end points.Step 4: Crop and adjust videoSelect one video clip and click on the Crop button to crop it. Select one or more videos, and click on the Video Adjustments icon to adjust the video effects.Step 5: Other editingThe editing tools also allow you to add text, effects, and audio effects. You can try out and play around with these tools to see how you want to edit your videos.