According to the invention, an obstacle avoidance radar based on an ultra-wideband cognitive CPPM signal generates a number of wide band CPPM signals which are orthogonal to each other. The signals pass through a transmitting beamforming module to form radar transmitting signals, and the signals are transmitted by a rectangular electron scanning array antenna of a receiving/ transmitting switch module. If another flight target carries out reflection, an echo signal is received by an electronic scanning array antenna to form a received signal, and the signal is collected by a signal acquisition module. A receiver matches a filter module to acquire the distance-doppler information of the target. The echo amplitude, the azimuth and the height information of the target are acquired through a two-dimensional multiple signal classification module. The information enters a Dirichlet process hybrid model clustering module for gather classification, and then different targets are distinguished through a generalized likelihood ratio detection module. The individual target information is sent into a variable point detection module to detect a mutational point in a target movement trajectory. According to the mutational point, the amplitude and the pulse width of the CPPM signals are redesigned, and the movement trajectory of an unmanned aerial vehicle is corrected to avoid collision with other flight targets.