SegmentEditor: How to keep the outline size the same?

I use SegmentEditor Module to add a segmentation and paint contour of nodule

and then, I export segmentation to file, reload it, show it’s contour of 2d view, the contour change smaller

How to keep the outline size the same?

Here you are seeing two different representations of the same underlying segmentation. One is the binary labelmap (above) with the stairsteps, and the smoothed polygonal reconstruction (below). If you save and reload and reload with the detaults the original labelmap will be preserved.

Also note that you can choose to show the closed surface representation in slice views: in Segmentations module → Display → Advanced → Representation in 2D views → Closed surface.