Abstract: 4004 brazing filler metal was used to vacuum braze 6063 aluminum alloy honeycomb plates, effect of different honeycomb core thickness on microstructure of brazed joints was investigated. The results showed that when brazing temperature was 585 ℃ and holding time was 20 min, honeycomb core with thickness of 0.1 mm could not be brazed. Three kinds of honeycomb core with different thickness had melting erosion phenomenon. When monolayer honeycomb core thickness was 0.10 mm and 0.15 mm, there was white Al-Si eutectic phase in the reaction zone of brazing interface, and its morphology was block when monolayer honeycomb core thickness was 0.10 mm and dendritic when monolayer honeycomb core thickness was 0.15 mm. When monolayer honeycomb core thickness was 0.21 mm, white Al-Si eutectic phase disappeared and only Si element enriched phase existed. When bilayer honeycomb core thickness was 0.10 mm, the brazed interface collapsed. When bilayer honeycomb core thickness was 0.15 mm, interface reaction zone (Si-rich intermetallic compound phase) was larger, but core material was not dissolved, and part of influence zone (α-Al solid solution phase) was also formed between interface reaction zone and core material. Influence zone between panel and interface reaction zone was also smaller than that of 0.10 mm bilayer honeycomb core thickness. When bilayer honeycomb core thickness reached 0.21 mm, influence zone between panel and interface reaction zone increased, core material also was not dissolved, and core material interface reaction zone became smaller. In other words, brittle Si-rich intermetallic compounds in bilayer honeycomb core decreased, and α-Al solid solution phase increased.