Hi Sun, so another note - if you can eliminate these edges completely:



That would be another simplification and cleaning step for the model, and would also simplify the fillet calculations quite a bit as well since there would be fewer edges colliding with one another throughout the model.

It looks like that edge is a juncture between 2 revolved pieces:



But this shape could be more simply and cleanly formed as just one larger revolved surface there instead of 2 identical ones joined together.

You can get that simpler shape there by deleting the existing surfaces there, drawing in a vertical line segment, doing a revolve (turn end caps off), and then joining the revolved surface into the other pieces, that's what I did to get the base shape in the attached 3DM file.

Having that as the base model will reduce quite a lot of edge junctures and small fillet pieces that the fillter would otherwise have to deal with.

As you've seen, filleting tends to be a rather sensitive area - filleting has a sequence of several complex operations that it has to do in a row, like offsetting surfaces, intersecting those offsets, building fillet pieces and potentially extending them and intersecting the extended pieces with each other, building corner patches between areas with kinks, ... it can run into problems if there is difficulty in any one of those steps. So the more simple structure (generally meaning the fewest edges and faces that are necessary) that you give it to work with, the better.

- Michael