Question: [![enter image description here](https://i.stack.imgur.com/vXXGd.png)](https://i.stack.imgur.com/vXXGd.png)

How can I smooth all crown but don't smooth the top of the crown? I did a subdivision surface, but this didn't work. All crown became smooth and changed form.

Answer: 
Another approach:

[![enter image description here](https://i.stack.imgur.com/SIHPD.jpg)](https://i.stack.imgur.com/SIHPD.jpg)

* Create a Z-scaled, subduvided UV sphere, and a capless cylinder, at the origin.
* Give the cylinder a few horizontal loops, and assign it a Srinkwrap modifier to the sphere; drag it down to a good-looking position in Z
* Select the N,S,E,W vertices on the top loop of the Cylinder, and with Proportional Edit / Linear falloff, drag the points up in Z
* Proportional off, Median Pivot Point, scale the bottom loop to 0 in Z
* Assign a Solidify modifier, with 'Crease' set to 1 for Inner, Outer, and Rim.

The crease will hold against any subdivision.. after applying the modifiers you can extrude down the cylindrical headband, etc. (You might not even need subdivision, maybe AutoSmooth will do..)

EDIT: .... But as moonboots points out, it's worth taking a little time to put in a bevel after applying the Solidify and a level of subdivision around the rims, and then across the peaks and troughs, as shown:

[![enter image description here](https://i.stack.imgur.com/DIBMy.jpg)](https://i.stack.imgur.com/DIBMy.jpg)
Here is a way to make a crown, maybe there's a simpler?

* Build a basic cube, delete its two side faces, give it a *Mirror* modifier.
* Drag up its central edge, add 3 vertical edge loops.
* Add some additional edge loops close to the angles so that it will sharp them later.
* Give your object an *Array* modifier. Choose a *Count* of 4. Enable the *Merge* option.
* Give your object a *Simple Deform* modifier / *Bend* mode. Choose an *Angle* value of 360°. If it doesn't turn around the Z axis, apply the rotation of your object.
* At last, give your object a *Subsurf* modifier (and press the *Smooth Shading* button on the *Tools* panel).
* Move a bit your edges with `G``G` to sharp the crest and the low of the crown.
* Apply the modifiers (except the *Subsurf* if possible), remove the doubles (where the 360° joint happens).

[![enter image description here](https://i.stack.imgur.com/ElpNJ.jpg)](https://i.stack.imgur.com/ElpNJ.jpg)