Jing,

And the soil likely needs changing to something more porous, too.

I am usually wrong about this, but it's in the perennial Sedum family, I think. As such, IME, it's much better in the ground, if you're able to grow it there.

Those flowers - are they of the plant in question?

The flowers on that are so pretty, like carnations.

Nope, they are not. Those are decoration only. Thank you all for the comments.

I like that - thank you so much for the photos - lovely.

Hello all, anyone know what is wrong to this rosette succulent? The leaves are fallen off easily, and found black stem nearer to the root. I dont know the name of it.

It is rotted badly. Likely overwatered - are there drainage holes in your containers? Water retaining soil and no drainage are very bad for your succulents.

You could possibly save top of it by cutting it off and repotting after letting it to callus first.

In a humid environment, water very very infrequently.