Hi tuananhnp, for Network to work it needs to be able to unwrap the curves into a regular grid similar to latitude and longitude lines on a sphere going to a flat world map.

The part that doesn't work in your current setup is you're missing the "poles" where longitude lines should end at a common point.

In the attached version I have split up 2 of your closed curves so that there are poles and so they can make a 2D grid and now Network should work.

You may get a better result though using an actual SubD box and using the SubD converter under SubD > Create > "From file".

- Michael