Abstract: Influence factors of rheological properties of rhodospirillaceae photosynthetic bacteria hydrogen production system were studied. The results showed that the degrees of biomass decomposition and utilization were related to bacteria quantity. Relative viscosity increased at first and then decreased with the hydrogen production time, and the optimum inoculation of photosynthetic hydrogen production was 20%-30%. Relative viscosity decreased with the temperature increasing. When the total mass of particles was constant, the interaction strength between the particles enhanced with the decrease of particle size, and the liquidity of the system decreased and relative viscosity increased. Meantime, when the concentration of ultramicro straw in the system increased, the particle spacing decreased, the effective volume ratio increased through collision, coacervation and polymerization among particles, and then the particles became very difficult to move freely. The relative viscosity increased with the increase of ultramicro straw concentration, which was benefit for photosynthetic hydrogen production. The results can provide a reference for research on mass transfer, heat transformation and velocity field distribution of photosynthetic hydrogen production system.