Abstract: A new slow-wave structure with two rectangular helixes is described in this paper. The high-frequency characteristics including dispersion characteristic and coupling impedance are calculated using 3D electromagnetic simulation software. The result shows that, compared with single rectangular helix SWS, double rectangular helix SWS is capable of higher coupling impedance in the same position with little dispersion characteristic change. Meanwhile, sheet electron beam can be set in the region containing these positions to further improve the output power. Key words: double rectangular helix slow-wave structure; micro-electro-mechanical system technology; sheet