The present invention provides a method for culturing photosynthetic bacteria, which belongs to the biotechnology field. The method adopts a large cement pool as a culturing container and uses a transparent plastic film to cover and seal the surface of liquid photosynthetic bacteria culture in the cement pool, and the photosynthetic bacteria are cultured under the irradiation of sunlight with average temperature larger than 20 DEG C. After culturing is started, the photosynthetic bacteria culture is sampled everyday in order to measure the pH of the photosynthetic bacteria culture, and by adding acetic acid solution with concentration between 5 percent and 30 percent into the photosynthetic bacteria culture and uniformly mixing, the pH of the photosynthetic bacteria culture is decreased to 7.0. The method can culture the photosynthetic bacteria on a large scale and promote the photosynthetic bacteria to grow rapidly and constantly, the dry-weight concentration of the finally obtained Rhodopseudomonas palustris cells is 1.8g/L, and the corresponding cell concentration reaches 81.8 multiplied by 10<8>/ml. The method realizes the purpose of rapidly and efficiently culturing high-cell-concentration photosynthetic bacteria on a large scale.