Abstract: Polypyrrole (PPy) is a photothermal conversion material with high efficiency and broad-spectrum absorption of sunlight. Polypyrrole chitosan (PPyCS) composite aerogel was prepared by freeze drying and applied to the solar water evaporation system. The preparation process of polypyrrole was optimized by controlling the crosslinking degree of aerogels and the polymerization time of polypyrrole. Results showed that the excellent photothermal conversion performance of PPy made the PPyCS composite aerogels with high absorbance (97.83%). Under the light intensity of 1 kW/m², the crosslinking agent (glutaraldehyde) was 150 μL, and polypyrrole reacted for 3 h, the composite aerogels achieved the best value. The evaporation rate was 2.6 kg/ (m²·h) and the photothermal conversion efficiency was 97.63%. Under the light intensity of 1 kW/m², the composite aerogel had higher evaporation rate (1.129 kg/(m²·h)) for natural seawater. After the 5 repeated tests, the photothermal conversion efficiency of the composite aerogel basically remained the same for the simulated seawater desalinated with 1 000 mg/L concentration. The water quality after treatment reached World Health Organization (WHO) drinking water standard.