Be aware that the video you referenced is from the training program TI was using about a decade and a half ago. I suspect that it was posted without TI's permission, which would mean that posting it constituted a violation of TI's copyright.
One of the problems we had with that drill sequence was that it tended to addict swimmers to the use of fins. You may have better experience with our current drill sequence, which is contained in this DVD:
here are some problem:
1. when i'm pulsing my chest, just can't help kicking my leg, is this normal?
Pressing your chest into the water is supposed to initiate a pulse that travels all the way down to your toes.
2. maybe my ankle doesn't have flexibility, i bought fin and expected some progress, but it doesn't work for me, i can't move forward without fin, even worse, i move back when i tried do the head-lead dolphin. could i ask for some suggestion from you? or just practice more?
We no longer use head-lead dolphins, nor do we have people do lots of laps of body dolphins, since many swimmers found it difficult to do this without wearing fins. I would suggest that you try only doing a few pulses at a time, then stopping, standing, and starting again. When you proceed to the drills that involve your arms, you should have less of a problem.