In this study, a cationic block structure with a strong neutralizing ability was formed through template polymerization. Acryloxyethyltrimethyl ammonium chloride (DAC) and acrylamide (AM) were used as monomers, and the ionic homopolymer sodium polyacrylate (NaPAA) was used as the template. The product containing NaPAA after template polymerization is denoted as NTP, whereas the copolymer obtained after removing the NaPAA is denoted as TP. The common polymer (denoted SP) of AM and DAC was copolymerized through solution polymerization. TP and SP were characterized and compared by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), H-1 nuclear magnetic resonance (H-1 NMR) spectroscopy, and thermogravimetric analysis (TGA). The results of H-1 NMR spectroscopy and TGA showed that a cationic block structure was formed in TP. The mechanism of the cationic block polymer used in water treatment was extensively studied through a jar test in which turbidity, zeta potential, and average floc size were used to evaluate the flocculation performance. The results further supported the cationic block structure of TP. TP, with a different structure than SP, resulting in a stronger neutralization ability, showed a better performance in flocculating kaolin suspensions. The dominant mechanisms for TP flocculation behavior at pH 5, 7, and 9 might be patching, charge neutralization, and bridging adsorption. The flocculation performance of NTP was not acceptable, whereas acidic NTP at pH < 2 showed a flocculation effect similar to that of TP.