To verify the electromagnetic interference effects of multi-rotor UAV in semi-airborne transient electromagnetic exploration, and develop effective noise reduction methods to improve the quality of exploration signal data.Methods: The time-frequency noise analysis is carried out to detect the electromagnetic interference generated by multi-rotor UAV (taking DJI T20 as an example) under different working conditions.The influence of the distance between the noise source (UAV) and the receiving point on the noise level is studied.A recursive least square method based on moving window is proposed and applied.Results: It is found that the main frequency band of periodic electromagnetic interference generated by motor rotation of DJI T20 UAV is 550~900 Hz.When the distance between the receiving coil and the UAV is 10m, the above interference can be ignored.Noise reduction experiments prove that the proposed adaptive noise reduction method can suppress the interference effectively and restore the original characteristics of the signal.Conclusions: It is proved by experiments that the electromagnetic interference of multi-rotor UAV in semi-airborne transient electromagnetic exploration can be observed, especially at close range.By applying recursive least square method based on moving window, the electromagnetic interference generated by UAV can be effectively reduced and the original characteristics of the disturbed signal can be restored.The application of the noise reduction technology to actual geological exploration data processing can significantly improve the data quality, and is conducive to further geological interpretation and mineral resource evaluation.