To test biomass of photosynthetic bacteria (PSB) in water, and to provide a way of PSB sewage reclamation, this paper adopted HPLC to analyze the concentration of CoQ₁₀and thus obtained the concentration of PSB in water. The results show that the chromatographic condition is as follows: The chromatographic column is SphherisorbC18 (10 cm×4.6 mm ID); methanol-absolute alcohol (9∶1) as mobile phase at a flow rate of 1 mL／min; column temperature 35 ℃; Wave Length of UV detector 275 nm; sample size 15 μL; column pressure 16.4 MPa. By extracting 5 h with acetone, volatilizing acetone completely and dissolving it with absolute alcohol, this method may obtain the maximum relative extraction of CoQ_10. The average recovery ratio of external reference method is 99.13％ and RSD 0.81％. The highest radiance-extraction is acetone extraction 5 h before evaporating completely and then solving in ethanol. The concentration of CoQ₁₀ in PSB in various cultural conditions and growing phases is quite stable. The impurities or microbes in wastewater do not affect the testing result. The concentration of PSB is (Y+37.487)／25.431 g·L^-1, Y is peak area(V·s). This method is simple and accurate, and can be used for quantitative analysis of PSB in water.