A multichannel UWB-based radar life detector includes a transmitting antenna and three receiving antennas for forming three radar echo signal channels. A 2-dimensional positioning method thereof includes: a1) amplifying weak life signals of stationary human by the channels, providing an 8-point integration method with an interval of 4 points to radar echo signals by distance; then breaking the integrated signals for decomposition and reconstruction in such a manner that target echo signals and three distance signals are formed; providing digital filtering and differential to the target echo signals for amplifying the weak but useful life signals; a2) 1-dimensionally distinguishing the signals by distance, analyzing spatial frequency according to the filtered and differentiated target echo signals as well as the distance signals for obtaining three target projection signals in the three channels; and a3) identifying the 2-dimensional position information of the targets according to the projection signals, forming an image.