The flow field of a submerged impinging stream mixer with two opposite nozzles was measured by non-intrusive planar laser induced fluorescence and two-dimensional high-speed particle image velocimetry techniques, and the flow field under different momentum ratios (M) and nozzle spacings (L/d) was decomposed further using proper orthogonal decomposition analysis for extracting the large scale structure in the flow. The results show that the energy of instantaneous flow field in the impinging stream is concentrated in the first order model, in which the momentum ratio of two jet outlets at M=1 accounts for 50% in the total turbulent kinetic energy, which is the highest proportion. 2%~5% in the total turbulent kinetic energy belongs to the second order model, 2% to the third order model, and there is almost no difference in the fourth order model. The highest proportion is about 38.6% at L/d=3. Obvious coherent structure that is located in the region near the non-stable radial jet exists in impinging stream low order intrinsic mode and large scale flow structure is directly related to the energy distribution of flow field, and the higher order intrinsic mode represents the flow of small scale structure. The large scale coherent structure is directly related to the liquid phase mixing behavior of the impinging stream, the larger scale coherent structure in the flow field helps achieve greater energy, which benefits the fast mixing of liquid phase.