A scheme of steppedfrequency radar that is uesd for building detection has been proposed,which solve the problem that the pulse throughthewall radar in the building layout inversion application of low resolution, the distance. The hardware platform of the scheme includes vector network analyzer, microwave RF control module, ultrawideband horn antenna and personal computer. Six ultrawideband horn antennas are arrayed by nonuniform interval, that the microwave RF control module was used to expand the channel and to achieve channel selection. LabVIEW is used to develop system software control platforms which achieves parameter configuration, data acquisition and online imaging processing. The experiments show that the system can be applied to different scenes of building wall imaging.