Abstract: LFM-Costas stepped frequency radar (SFR) signal is an important radar signal. This paper presents a method producing N-steps Costas sequence aiming at the need in LFM-Costas stepped frequency radar (SFR) signal, and builds many sets of 64-step Costa arrays according to practical needs. These Costas sequences are optimum discrete signals with good correlation characteristic. Coding with Costas arrays is combined with LFM stepped frequency radar (SFR) signal to generate LFM-Costas stepped frequency radar (SFR) signal. The ambiguity function is analyzed in detail. The results of theoretic analysis and simulation show that, by using this kind of signal, the ambiguity sidelobe is well suppressed and the range-velocity coupling in the stepped frequency radar is also significantly resolved.