This paper presents a sensorless control strategy for seven-phase non-sinusoidal permanent magnet synchronous machine (NSPMSM) with high frequency signal injection (HFSI) method in 5th harmonic subspace. Seven-phase nonsinusoidal machine benefits high torque density due to the use of third harmonic components. Firstly, two torque generation strategy in different harmonic subspaces with the minimum injected rms value and amplitude of current is deduced in this paper. Secondly, in order to reinforce the reliabilities of multiphase machine, the HFSI sensorless control is employed. Comparing with traditional HFSI method, the proposed control strategy is achieved in 5th harmonic subspace, which can avoid the torque ripple caused by the injected signal. Finally, according to simulations results the two torque distribution method is validated and compared and the effectiveness of the HFSI method is verified.