The edge of the Volume object.

[dongju.jeong]

It looks natural from the sky.

 

But when I look from the side, the boundary stands out at the edge.

Is there a way to soften the boundaries?

[silent]

dongju.jeong

For the views from ground it's better to use Physically-based fog that you can set up in the Environment settings. Proper ground fog objects is still in the development and not yet available out of the box.