The three-dimensional flow fields both in front and at the back of the rotor of a low-speed axial compressor are measured in detail and the contrastive analysis is performed in a state of approximative stall and stall by utilizing a five-hole probe. Based on the dynamic variable curve of the static pressure on the surfaces of the casing in the entrance and the exit under the condition of a stall state, the spatial structure of the stall region and the dynamic characteristic of flow parameters are researched, a differential equation model is established to describe the dynamic process of the airstream in a stall state, and the model is also validated by the experimental data. The results show that the backflow happens in the stall region, the included angle between the backflow speed and the partial airstream in direction is 110°. The radial scope occupied by the backflow region exceeds the blade tip region by 70%, and the axial scope is the span in front of the stator. The flow parameters, such as pressure and velocity etc., fluctuate damply with time in the stall region, and the dynamic variable process can be described by a two-order system.