The distance ambiguity function of Pulse Frequency Encoding Signal (PFES) has grating lobes around the main lobe, under the circumstance that the width of sub-pulses is larger than reciprocal of minimal frequency hopping gap.Grating lobes not only have bad effect on accurate detection of single target, but also hide the main lobe of weak target when it locates in grating lobes of others, leading to miss detection.In order to eliminate the grating lobes of distance ambiguity function of frequency-coded sub-pulses signal, sub-pulses Linear Frequency Modulation (LFM) was introduced based on the original signal, then parameter choice rules of the composite signal were discussed to achieve that purpose.The effect of the method was verified by using Matlab simulation.