To investigate the unsteady flow characteristics in side channel pumps, the vortex structures and their evolutions in the impeller and side channel flow passages have been comprehensively studied. Systematically, three impeller schemes were designed with different ratios of convex blade height h to impeller blade length l (h/l=0.2, 0.5, and 0.8) for detailed analysis. The findings indicated that the convex blade broadens the high-efficiency range and improves the efficiency at the best efficiency point for scheme h/l=0.2. Impeller scheme h/l=0.2 records the highest vortex concentration region, scheme h/l=0.5 displays as scattered spots, while scheme h/l=0.8 exhibits significant flow pattern changes in the impeller. The vortex distribution area and vortex intensity in the lengthways between the impeller and side channel of h/l=0.2 are almost analogous, but the other two impeller schemes have obvious separation and very chaotic. Although the shrinkages of axial vortexes in the impeller did not reflect on hydraulic performance, impeller schemes h/l=0.5 and 0.8 provided an outstanding performance in reducing the pressure fluctuations. The objective of this study is to provide a theoretical basis for optimal design and analysis of strong vortex flows in side channel pumps.