The excitation intensity and excitation duration are the essential experimental conditions of the high-frequency flash method for the measurement of algae photosynthetic parameters. The fraction of reduced primary electron acceptors and the reoxidation extent of these reduced primary electron acceptors were analyzed under different excitation intensities and excitation durations. The analysis results indicate that 30 000 μmol quanta·m-2·s-1 is the optimal excitation intensity and 70 μs is the optimal excitation duration. Under this optimal excitation condition, 96.08% of the primary electron acceptors are reduced and only 9.81% primary electron acceptors reoxidize.