A electronic blackbody cavity is provided. The electronic blackbody cavity comprises an inner surface; a chamber surrounded by the inner surface; an opening configured to make an electron beam enter the chamber; and a porous carbon material layer located on the inner surface. The porous carbon material layer consists of a plurality of carbon material particles and a plurality of micro gaps. The plurality of micro gaps are defined by the plurality of carbon material particles. A secondary electron detection device using the electronic blackbody cavity is also provided.