A full-spectrum covering ultra wideband full-photonics based radar system, comprising a signal transmitter, a transceiver module, and a signal receiver; wherein the signal transmitter comprises a mode-locked laser, a first dispersion module, a first optical coupler, a second optical coupler, a first optical filter, a second dispersion module, a second optical filter, a first tunable time delay module, a third optical coupler, an optical amplifier, and a first photodetector; the transceiver module comprises a band selector, a first electrical amplifier array, a T/R component array, an antenna array, and a second electrical amplifier array; the signal receiver comprises a third optical filter, a second tunable time delay module, an electro-optical modulator, a third dispersion module, a second photodetector, an analog-digital conversion module, and a signal processing module; an output end of the mode-locked laser is connected via the first dispersion module with an input end of the first optical coupler having a first output end and a second output end: the first output end of the first optical coupler is connected with an input end of the second optical coupler, the second optical coupler splits an optical path into a first optical path and a second optical path, with the first optical path traversing successively the first optical filter and the second dispersion module till an input end of the third optical coupler, the second optical path traversing successively the second optical filter and the first tunable time delay module till the input end of the third optical coupler; the third optical coupler couples a signal of the first optical path and of the second optical path respectively into one optical signal and outputs via the optical amplifier to enter the first photodetector, the first photodetector converts the optical signal into an electrical signal and inputs to an input end of the band selector of the transceiver module, the band selector having more than 2 output ends, with each said output end of the band selector connected successively with a respective electrical amplifier of the first electrical amplifier array, a respective T/R component of the T/R component array, and a respective antenna of the antenna array to form a channel for a respective waveband; an echo signal of an electrical signal transmitted from the antenna array is returned by a to be detected target and passes successively via the respective antenna of the antenna array, the respective T/R component of the T/R array and the second electrical amplifier array to form a target echo electrical signal to be inputted to an rf input end of the electro-optical modulator; an optical signal of the second output end of the first optical coupler successively passes via the third optical filter and the second tunable time delay module to be inputted into an optical input end of the electro-optical modulator to form an optical pulse carrier wave; the electro-optical modulator loads the target echo electrical signal onto the optical pulse carrier wave to form an echo modulation optical signal corresponding to the target echo electrical signal, with the echo modulation optical signal of the electro-optical modulator successively passing via the third dispersion module, the second photodetector, and the analog-digital conversion module to enter the signal processing module.