Hello - the existing surfaces are something of a mess - the edges are way out of tolerance:
and the file tolerance is too large anyway, at .1. Please see: https://wiki.mcneel.com/rhino/faqtolerances for more information on tolerances. Once you get that sorted out and the model cleaned up, BlendSrf would be the first tool to try.
Sorry for the late reply. I gave up using networksrf with the original surfaces, but i replaced to new surfaces again and did with 2 rail sweep instead. i set 0.1 as tolerance and it works. surfaces are still not neat but it got much better.