how to get random but smooth model like this image?

I need some models like above image. The surface is like a random-shape stone, and the normal of the surface is smooth.
Is there anyway to model these mesh? Thanks.

Take a sphere and grab some vertices with proportional editing: push and pull at wil…

Another way is to Add a cube (or other base mesh), subdivide, To Sphere (Ctrl+Alt+S) to give some roundness, subdivide again with a little fractal noise to give randomness, smooth shading and subdivision surface modifier to give final smooth outline.

Thanks for so quick reply. I read a paper, and their method is that:
Object was generated at random by distorting spheres with an initial radius of 8 cm. This transformation was accomplished by a series of sinusoidal perturbations on the surface at random orientation. The resulting objects were smoothly curved with no discontinuities.
I have tried proportional editing before, but the mesh is somehow not smooth because manually push and pull is not accurate as sin function.

you could also add 2 displacement modifier to get big and small details on the object


Yeah, I’d recommend displacement modifiers. The default “add extra texture” cloud texture should do the trick. If you use Object Coordinates connected to an Empty, you can easily tweak the texture size by scaling the empty. And produce any number of unique shapes by duplicating and moving the mesh in relation to the empty.

Maybe I misunderstand what the goal is, though… I’m not sure how well the described methods correspond to the sinusoidal perturbation stuff. But have lots of potential variation if you start changing and tweaking the displacement texture.
(example: just bump texture contrast to 5 for a fun semi-hard bubbly effect)

All tips are OK, so just to complete a list there is a Rock Generator.
If you need just this chui shape - subdi, displace with empty, subsurf sounds better