The FDTD method is used to calculate the specific extinction cross section of the powder of brass 70Cu/30Zn with 1.35×104to 2.56×105particles in the infrared frequency range. A digitized model of body‐center‐like structures is used for the calculations of specific extinction cross‐section. From theoretical calculations, the value of a specific extinction cross section of the powder of brass 70Cu/30Zn is between 0.14 to 4.0 m2/g. While the experimental measurement shows the value of specific extinction cross section to be between 0.58 to 3.78 m2/g. The theoretical results concur with those obtained from the experimental measurement for the cell sizes of particles in the range of 0.05 to 0.4 p.m. There are some differences between the theoretical value and measurement data of specific extinction cross section for other particle sizes outside the range of 0.05 to 0.4μm.