The effects of additive polyacrylamide (PAM) on combustion characteristics of Al-H2O-based propellants are investigated in air at atmospheric pressure. The combustion process and flame phenomena are recorded by a high-speed photography technique, and the condensed combustion products are analyzed by scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDS). The results show that PAM is beneficial to improve the combustion performance of Al-H2O-based propellants. The mixture of nano-sized Al powder and H2O or H2O with 1 wt% PAM can be ignited, but the combustion is not a self-sustaining process. The mixture of nano-sized Al powder and H2O with 3 wt% PAM can be ignited with a self-sustaining combustion. Its burning rate is 4.07 mm/s. The mixture of nano-sized Al powder and H2O with 3 wt% PAM still retains combustion when 33% nano-sized Al powder is replaced by micron-sized Al powder, while the burning rate is reduced to 0.5 mm/s. This work promotes a better understanding for the combustion processes of Al-H2O-based propellants.