The invention provides a passive interference suppression method in a complex environment based on cognitive radar waveform design. The passive interference suppression method comprises the followingsteps: a radar transmitting and receiving signal model is determined; response prior information of a target, clutter, passive interference and noise is determined; a detector is determined and detector performance is obtained; and waveform design is carried out according to the bandwidth and the transmitting energy, and transmitting signal frequency domain energy distribution is calculated, wherein the obtained signal frequency domain energy spectrum is used for transmitting signals. Through the clutter and passive interference confrontation-oriented waveform design, the interference suppression-oriented energy distribution mode can be designed in an ultra-wideband frequency domain based on the prior information of clutter and passive interference, so that the interference response is suppressed, and the target detection and recognition capability of the radar under complex environmental conditions is improved.