First,the general theoretic model of micro-Doppler and the micro-Doppler signatures of ballistic targets are displayed,and then six problems of micro-Doppler which are low and high carrier frequency,narrow band and wide band,return time and illuminating time,coherence,resolution as well as velocity and acceleration are studied under the case of the micro-Doppler induced by coning.The research results are valuable for the extraction of micro-Doppler and the design of radar parameters.