The invention discloses an ultra-compact snapshot type polarization imaging detecting device and a detecting method. The detecting device comprises a lens array and a detector which are successively arranged in an incident light direction. A polarizing interferometer is arranged between the lens array and the detector or is arranged in front of the lens array. The polarizing interferometer comprises a line polarizer, a single-wedge-shaped birefringence prism with a wedge angle of beta and a line analyzer. The transmission directions of the line polarizer and the line analyzer are same and areat an angle of 45 DEG to the quick axis direction of the single-wedge-shaped birefringence prism. The line polarizer is arranged in front of the single-wedge-shaped birefringence prism. The light sensing surface of the detector is in the back focal plane of the lens array. The detector of the detecting device can acquire an interference image array of different corresponding light path differencesin one exposure period, thereby realizing no requirement for sampling of interference images which are symmetric relative to a zero light path difference. The number of the interference images is farsmaller than the sampling number required for satisfying a Nyquist's theorem. Spatial resolution is improved, and a polarization spectrum image with high spectrum resolution can be reconstructed by means of a compressed sensing algorithm.