The present disclosure relates to a downhole rotating magnetic field generator, wherein a stator assembly is formed by fixedly connecting a guiding stator, windings, and a body together, and a rotor assembly is formed by mounting a turbine rotor and a permanent magnet together. Between the stator assembly and the rotor assembly, sliding bearings are arranged and small mud passages are formed. There is no metal isolation between the rotor and the stator for cutting through the magnetic lines of force, so that the eddy current loss is relatively small. Meanwhile, with mud flowing through the passages as lubricant, overheating of the generator can be prevented and high power output can be ensured.