Character movement on the other Object which is moving ?

I have a problem with my game. Hope everybody can help me to solve it.

In my game, i have a character which is standing on the other object and that object is rotating around the origin O (0,0,0). When i start the game, the object move. However the character still stand on the same position as before, until the object doesn't below the character and then the character fall down. So, how can my character stand and walk on the object?

my rotation script:

 public float speed;
 private Vector3 point = new Vector3 (0f, 0f, 0f);
 private Vector3 rotationVector = new Vector3(0f,5f,0f);
 private float wise =-1;
 void Update () {
     transform.RotateAround (point, rotationVector , 2 * Time.deltaTime* speed * wise);
 }

sory, I am not very well about writing!