Abstract: In order to improve the axial resolution and satisfy the contrast resolution of medical ultrasound imaging, a predistorted Linear Frequency Modulation (LFM) coded excitation new method based on amplitude weighting is proposed. Combining the amplitude weighting technology of LFM transmitted signal with the sidelobe reduction technology of echo signal, the method on the one hand can compensate the influence of transducer impulse response on transmission signal, so bandwidth of the echo signal is not limited by the transducer and axial resolution is improved. On the other hand, the method can remove the Fresnel ripples of transmitted signals frequency response, increase its bandwidth and use mismatched filter for pulse compression, so range sidelobe is suppressed to ensure contrast resolution. The results of simulation reveal that in contrast with constant envelope LFM coded excitation, the predistorted one can improve axial resolution and reduce maximum sidelobe at -48 dB to satisfy contrast resolution of medical imaging. FieldII Simulation results of B-mode image show that the axial resolution of constant envelope LFM coded excitation and the predistorted one is 0.35 mm and 0.25 mm, respectively.