this is the way to improve french. we have to watch film more than 3 times at least. it's useful

The problem is that, when there are subtitles, it can often be tempting to read and concentrate on the subtitles only and, by doing so, not paying attention at what is being said!

sometimes, when we watch a french movies, we don't understand all words that actors say so for that french movies with french subtitles is useful

I watch French movies with subtitles in English. I watch English language movies with French subtitles.  I find it helps.