Due to high speed moving of the target, the wideband radar echoes after dechirping is a multi-component LFM signal. Directly using the fast Fourier transform (FFT) to implement pulse compression, the high resolution range profile (HRRP) will be broadened and distorted. To improve the quality of the HRRP, considering the fractional Fourier transform (FRFT) is the generalization of the FFT with good concentration for the LFM signal and without cross-term interference, we substitute the optimal FRFT for the FFT in the conventional HRRP imaging method and propose a new imaging method. For the proposed method, selecting the optimal order of the FRFT is important and a fast search algorithm based on fractional autocorrelation is employed in this paper. Compared with other HRRP imaging methods with the motion compensation, the proposed method not only is easy to perform without involvement of complex motion compensation, but also can correct the phase distortion, which is important for the following ISAR imaging process. Furthermore the method has low computational cost and good robust property for additive noises. Experimental results show the effectiveness of the proposed method.