Abstract: Multi-subband signal splicing is an important way to achieve the ultra-high-resolution of spaceborne synthetic aperture radar （SAR） in range. However， due to the non-ideal factors of hardware and atmosphere affections， there will be amplitude and phase errors in the received sub-band signals， and amplitude， phase and delay inconsistency errors between different sub-bands. These errors will seriously affect the quality of multi-subband splicing signal and final SAR image. Based on the model of spaceborne multi-subband SAR system， this paper first proposes an imaging processing strategy， i.e.， subband imaging and multi-subband splicing. Then， an error estimation and compensation method based on strong points data is proposed for the amplitude， phase and delay errors intra and inter subbands. This method mainly includes four steps： strong points data extraction based on quality phase gradient autofocus （QPGA）， intra subband error estimation based on PGA， inter subband error estimation and spectrum splicing. Finally， the effectiveness of this method is verified by theoretical simulation data.