As one of microwave absorbing materials, SiC nanowires have a good microwave absorbing property, a wide microwave absorbing bandwidth and a low density. However, the poor impedance matching condition and low conductivity of SiC affect the improvement of its microwave absorbing property. To adjust the electronic structure of SiC and improve its electromagnetic properties, La3+ doped SiC nanowires were synthesized via carbothermal reduction at 1 600 ℃ with silicon powder, activated carbon and La2O3 powder as raw materials. The results show that doping La3+ can increase the aspect ratio and stacking fault density of SiC nanowires, and enhance their ability to form three-dimensional network structure and interface polarization, and improve their dielectric properties. At 2-18 GHz, the real part of permittivity increases from 3.08-13.48 (x = 0) to 3.33-19.75 (x = 1.0%), and the imaginary part of permittivity increases from 3.45-6.98 (x = 0) to 5.03-11.56 (x = 1.0%). Also, La3+ doping improves the conductivity of SiC nanowires and enhances its conductivity loss. SiC nanowires doped with 1.0% La3+ achieve a minimum reflection loss (RL) of -31.29 dB with the thickness of 2.0 mm and the effective absorption bandwidth with RL<-10 dB of 7.18 GHz due to the simultaneous enhancement of interface polarization and conductivity loss of SiC nanowires. The electronic structures of SiC nanowires and La3+ doped SiC nanowires were analyzed via the first-principle calculations. The results show that the band gap of SiC nanowires decreases after La3+ doping, verifying the enhancement of their conductivity. La3+ doping can increase the stacking fault density of SiC nanowires and solve a problem that the stacking fault density decreases. The results of this study can provide an idea for the synthesis of SiC nanowires with a high electromagnetic absorbing capability.