Abstract The door is the main part of the side wall of the vehicle body and the key to the side explosion protection of the vehicle. First of all, this paper takes a certain type of armored vehicle as the research object to analyze the side blast protection performance of the equivalent composite door based on the sandwich structure with a negative Poisson’s ratio core layer. Then, the effect of the cell length, cell height, cell angle, cell thickness, and thickness gradient of the core layer on the explosion protection performance of the sandwich structure is studied. Finally, the door structure is optimally designed based on the basic structural parameters of the cells. The results show that the side blast protection of the vehicle is improved compared with the original door, and the shoulder and head injuries of the occupants under side blast impact are reduced to a great extent.