The invention discloses a low-altitude target detection broadband radar system based on pitching MIMO and an array optimization method. By combining the frequency phase position comprehensive coding synthetic broadband signal processing technology and the sparse MIMO array signal processing technology, highly efficient and high-precision detection on a low-altitude target can be achieved. The system comprises an antenna branch system, a transceiving assembly branch system, a radio frequency channel branch system, a waveform generation branch system, a frequency synthesizer branch system, a signal processing branch system and a display control terminal branch system. The waveform generation branch system generates six-channel middle-frequency signals through a digital-to-analog conversion DAC playing board card. The middle-frequency signals are in the form of frequency phase position composite coding signals. The six-channel middle-frequency signals enter the frequency synthesizer branch system and pass through the radio frequency channel branch system, the transceiving assembly branch system and ten antenna branch system, so emission wave beams are formed. The transceiving assembly branch system receives echo signals of the target. The echo signals pass through the radio frequency channel branch system, the frequency synthesizer branch system and the signal processing branch system, so an one-dimensional distance image and primary point tracks are obtained.