Abstract: With the development of wideband radar technology, the narrowband ambiguity function (NAF), which is based on the narrowband echo model, is not effective to analyze the signal process issue of moving target echo. To solve this problem, the wideband ambiguity function (WAF) of stepped frequency (SP) waveform is proposed based on wideband echo model. The property of wideband ambiguity function was studied, from which we could prove that NAF is just an approximate to WAF under low velocity condition. Making use of WAF match point characteristic, a target detection method based on the amplitude of match point was advanced. Simulation results verify the effectiveness of the method.