Nguyenthienchan, please make sure you read the thread I posted about vibrato. Scroll up a little and find the link in a big box. It says: What’s Important When Starting to Learn Vibrato.
I’m not 100% sure about the problem you are having, but I can give some general ideas. I don’t advise using a metronome, but I have had students practice a vibrato motion with measured, slow vibrato motions. Keep this in mind: If what you are doing is too hard, simplify it. So I have students do this simple arpeggio, two long 1/2 notes per note, slow, big tone, memorized.
D3, A1, A3, E2 (g natural), E3, E4, E3, A3, A4, A3, A1, D3
Once memorized, roll each finger back and TO the pitch, rhythmically, TWICE. Two rolls per note/ bow. Third finger is easiest, because it is a weak, loose finger. One is tight. Four is weak and distant. Both those fingers are less easy. Two should be pretty easy also.
When that’s easy, double the rhythm, rolling four times on each note/bow. After that, you will double it again, but you wont count rolls, you will just double the motion speed.
If you are finding that your fingers are tensing up still, please simplify. Practice vibrato on A3 only. Make sure you are doing the right motion. (refer to the link above) and then, release the violin thumb from the neck so that during the A3 vibrato, you are only touching the violin with the third finger tip. Let me know if this helps you!
If you dont want to measure the rhythmic rolls, practice vibrato motion without a timed beat, but make sure it is wide enough and still slow. Keep the thumb in place. When you feel tension, release the thumb, continuing the vibrato motion. Eventually, do this on all strings, with all fingers. Good luck!!