There are two typical difficulties in radar detection of uncooperative targets: weak target and unknown velocity. Coherent pulse integration method is used in detecting the weak target, but it needs to detect the target velocity accurately and compensate the velocity, therefore it is limited in practical application. A design method of coded stepped frequency chirp waveform is proposed, which can integrate the pulse when the velocity is unknown and synthesize the wideband after the velocity is measured accurately. Firstly, the range velocity coupling characteristic of Linear Frequency Modulation(LFM) is studied, and the range migration is compensated by waveform parameter design. Then, the wideband synthetic technology of the stepped frequency chirp waveform is studied in order to get high resolution range profile without range ambiguity. Finally, simulation experiments validate the advantages and practical value of the proposed waveform.