An ultra-wide-band multi-mode radar signal generation method used in modern imaging radars comprises the following main steps: 1) generating a single-narrowband digital intermediate frequency signal by a data signal source; 2) filtering out-of-band interference signals in the signal generated in step 1; 3) spreading spectrum and carrying out up conversion on the signal obtained in step 2; 4) collecting and analyzing the signal obtained in step 3 by using a general instrument; 5) evaluating whether the signal satisfies requirements according to the step 4, if the signal does not satisfy the requirements, carrying out predistortion to the digital signal source, returning to step 1 and circulating from the step 1 to the step 4 till the signal satisfies the requirements so as to complete the generation of the ultra wide band signal. The invention also provides an apparatus which is used to realize the above method. In the method of the invention, spread spectrum is adopted to obtain the ultra wide band radar signal under a low sampling clock; a plurality of work modules, which are a plurality of different bandwidths and pulse widths radar signals, can be completed. The invention plays an important role on raising radar imaging resolution and enhancing radar system flexibility.