In this study, a method was presented to accurately obtain the extinction characteristics of the non-spherical biological particle aggregates. Based on the multi-sphere particle model of non-spherical particles, a randomly oriented aggregation model was firstly built to construct the aggregates. The discrete-dipole approximation method was used to calculate the extinction characteristics of aggregates in the 3–14 µm waveband. The average mass extinction coefficients of three materials are $0.802{\mathrm{m}}^2/\mathrm{g}$, $0.907{\mathrm{m}}^2/\mathrm{g}$, and $0.866{\mathrm{m}}^2/\mathrm{g}$ in the 3–5 µm waveband and $0.590{\mathrm{m}}^2/\mathrm{g}$, $0.402{\mathrm{m}}^2/\mathrm{g}$, and $0.523{\mathrm{m}}^2/\mathrm{g}$ in the 8–14 µm band, respectively. Smoke chamber experimental results are in good agreement with theoretical analyses.