A terahertz detector comprising a planar array structure that is constituted by a plurality of pixel units, wherein the plurality of pixel units each comprise N sub pixels and each of the sub pixels comprises no more than one signal trigger configured to transform a terahertz signal to an electrical current pulsing signal, and each of the plurality of pixel units detects a signal that is a sum of the electrical current pulsing signals of the N sub pixels, where N is an integer greater than 1; wherein the N sub pixels of each of the pixel units are connected in parallel; wherein each of the sub pixels comprises: a sensitive unit configured to transform a terahertz signal received to an electrical signal; and a Geiger avalanche photodiode; and wherein the sensitive unit is electrically connected to the Geiger avalanche photodiode, and the sub pixel is configured: such that the Geiger avalanche photodiode is in an initial breakdown state under a bias voltage in a case where the sensitive unit receives no terahertz signal, and such that in a case where the sensitive unit receives a terahertz signal, the sensitive unit transforms the terahertz signal to an electrical signal that is detectable and the electrical signal is further transformed to a voltage signal and then is applied to the Geiger avalanche photodiode so as to excite the Geiger avalanche photodiode to avalanche and output a transient electrical current pulsing signal. wherein the N sub pixels of each of the pixel units are connected in parallel; wherein each of the sub pixels comprises: a sensitive unit configured to transform a terahertz signal received to an electrical signal; and a Geiger avalanche photodiode; and wherein the sensitive unit is electrically connected to the Geiger avalanche photodiode, and the sub pixel is configured: such that the Geiger avalanche photodiode is in an initial breakdown state under a bias voltage in a case where the sensitive unit receives no terahertz signal, and such that in a case where the sensitive unit receives a terahertz signal, the sensitive unit transforms the terahertz signal to an electrical signal that is detectable and the electrical signal is further transformed to a voltage signal and then is applied to the Geiger avalanche photodiode so as to excite the Geiger avalanche photodiode to avalanche and output a transient electrical current pulsing signal. a sensitive unit configured to transform a terahertz signal received to an electrical signal; and a Geiger avalanche photodiode; and wherein the sensitive unit is electrically connected to the Geiger avalanche photodiode, and the sub pixel is configured: such that the Geiger avalanche photodiode is in an initial breakdown state under a bias voltage in a case where the sensitive unit receives no terahertz signal, and such that in a case where the sensitive unit receives a terahertz signal, the sensitive unit transforms the terahertz signal to an electrical signal that is detectable and the electrical signal is further transformed to a voltage signal and then is applied to the Geiger avalanche photodiode so as to excite the Geiger avalanche photodiode to avalanche and output a transient electrical current pulsing signal.