Abstract: For Frequency-Modulated Continuous-Wave Multiple-Input Multiple-Output (FMCW MIMO) radar, orthogonal waveform design is one of the most challenging technologies. The Beat-Frequency Division method splits the whole bandwidth of the dechirped signal into several subbands, and after band-pass filters one dechirped signal can be divided into multiple channels. However the spectral incoherence between the subbands and the complex of the system for the reason of wide band are significant drawbacks. In this letter, we presented a novel orthogonal waveform for FMCW MIMO radar based on Orthogonal Frequency Division Multiplex (OFDM) technique. With a frequency offset the waveform are orthogonal in M sweep periods, where M is the number of waveforms. After Discrete Fourier Transformation, the beat signal spectrums can be separated into multiple channels by means of Polyphase Decomposition technique. The proposed OFDM waveform needs no filters for division, so the system with better coherence becomes much simpler. At last the emulation of three orthogonal waveforms verified the proposed method.