Abstract: To study the impact of the polymorphic biological particles on the electromagnetic equipment such as target detection, the artificially prepared flocculent biological particles were equivalent to bullet rosette particles. Then the biological particles with different number and length of branches were built, and the discrete dipole approximation(DDA) method was used to calculate the extinction efficiency factor for biological particles. The results show that the structures of biological particles have great impact on the broadband extinction performance. The extinction performance of biological particles is positively correlated to the number and length of branches in the far infrared waveband and is positively correlated to its length of branches but independent of its number of branches in the millimeter waveband. Based on studying the relationship of extinction efficiency factor with the number and length of branches, the biological particles average extinction efficiency factor in the far infrared waveband was constructed. The model provides a reference for the further extinction performance study and morphology control of biological particles.