Is rope stretch has some limitation?

[josemendez]

But the rope seem too loose. I have tried to set the mass property in the rope path. But nothing change.

Mass has nothing to do whatsoever with stretching. It only affects how the rope interacts with other objects, just like in the real world.

Also I have changed the Bend Constraints - Maxbending to 1 in the ObiRope compoenent. It has changed a bit but still very loose. Could u give me some suggestion?

Bending != stretching. Changing the bending constraint parameters will not affect stretching in any way, just like changing stretching parameters won't affect bending. It's two completely different things.

Try increasing the amount of updater substeps, and/or the amount of distance constraint iterations, as explained in the manual:
http://obi.virtualmethodstudio.com/tutor...gence.html

Takeaway message from this section: If your rope/cloth/softbody/fluid is too stretchy or bouncy, you should try:

Increase the amount of substeps in the updater.
Increase the amount of distance constraint iterations.
Decrease Unity's fixed timestep.

I remember there a stretch scale property in the previous version can change it easily but can't find it in the 5.3 version

Stretching scale simply changed the rest length of distance constraints (shortening/lenghtening them), but did nothing in regards of stretching. Has been removed from 5.3 because it was highly unphysical, and caused more problems than it solved.