La_1-xSr_xMnO₃ nanometer powders were prepared by sol-gel method. The crystal structure, magnetic properties, electromagnetic properties and microwave absorption properties of LSMO with different doping amount of Sr^₂₊ were investigated. The results show that with increased amount of Sr^₂₊, the lattice constant and Mn-O-Mn bond Angle increase, while the average grain size decreases gradually and the complex dielectric constant increases first and then decreases. The LSMO changes from antiferromagnetism to ferromagnetism when Sr^₂₊ is doped. In the range of 2~18GHz, the best absorbing properties can be arrived when the doping amount of Sr^₂₊ is 0 and the thickness is 2mm. The effective frequency band corresponding to the reflectivity less than -10dB is 12.5~18GHz. The doping of Sr^₂₊ can make the absorbing bandwidth move to the low frequency availably. In the X-band, the effective bandwidth of the LSMO reaches 2.6GHz when the doping amount of Sr^₂₊ is 0.2 and the thickness is 2.3mm. It is proved that LSMO is a kind of dielectric loss absorbing material with excellent performance.