If the two surfaces were join-able, you would use RhinoJoinBreps(). But the edge one one surface does not match the edge of the other surface, within tolerance. You can use Rhino’s ShowEdges command to help you find the locations there the gaps are too wide. Try re-creating one of the surfaces (the one you probably made with Sweep2) using the edge of the other surface as a rail curve.
dale,the merge.rar I provided have two breps,
and had re-creating one of the surfaces using the edge of the other surface as a rail curve.
but still can’t join then to onebrep.
more information : I rebuild the rail curve with less control points(the edge of the other surface) before sweep2,I think maybe this lead to the gaps too wide.
but I realy need rebuild the rail curve,otherwise the surface will have too much iso curves.