The invention discloses an optimum design method of an upflow type anaerobic fermentation biological hydrogen production reactor and application of the optimum design method, and belongs to the technical field of environmental engineering. The optimum design method is used for studying internal flow regime characteristics of the reactor under different waterpower ascending velocity conditions and influences on the hydrogen production speed of the hydrogen production reactor caused by the internal flow regime characteristics on the basis of a numerical simulation method of a computational fluid mechanics technology. An Euler-Euler gas-liquid-solid three-phase fluid model is used for obtaining detailed flow field information such as a liquid phase velocity field, a solid phase volume fraction and a fermentation gas hydrogen component volume fraction, on the basis, a biochemical reaction kinetic model is coupled to carry out dynamic simulation and prediction on the hydrogen production rate of the reactor, and comprehensive analysis is carried out on different flow regime data obtained through simulation according to influences on the hydrogen production reactor caused by feedback of various flow fields so that the optimal waterpower ascending velocity can be determined. The efficient method is provided for optimal design of the upflow type anaerobic fermentation biological hydrogen production reactor. The optimum design method of the upflow type anaerobic fermentation biological hydrogen production reactor and application of the optimum design method have the advantages that technologies are mature and stable, the effect is visual, the period is short, and the cost is saved.