Spectrum analysis is the most important branch in radar signal processing and significant of radar target classification and feature detection. Having the special property, higher spectrum is very useful for us to analyse radar echoes from a new view. This paper presents double (Q, K) bispectrum algorithm for ultra-wideband radar echoes. Compared with other bispectrum estimation algorithm, simulation results show that the algorithm we presented here has significant improvement. At last, we cite an example for the application.