In order to improve the extinction performance of red phosphorus smoke to 10.6 μm laser emission,the extinction coefficients of nanometer alumina aerosols, red phosphorus smoke and their combined smoke to 10.6 μm laser emission were tested in a middle smoke chamber. Results show that, under the air relative humidity of 40%,the extinction coefficients of nanometer alumina aerosols, red phosphorus smoke and their combined smoke to 10.6 μm laser emission with incident power of 1W are 0.222 m²·g^－１,0.298 m²·g^－１ and 0.449 m²·g^－１, respectively. It indicates that nanometer alumina combined with red phosphorus smoke improves the diffusion performance of nanometer alumina remarkably, and the extinction coefficient of the combined smoke enhances by 50.7% than that of red phosphorus.