The techno-economic analysis of dark fermentative hydrogen production from molasses in a novel continuous mixed immobilized sludge reactor was performed. The hydrogen-producing plant was assumed to be built in Hangzhou with lifetime of 10 years. The effect of the working volume (10-50 m<SUP>3</SUP>) on the economic performance of hydrogen-producing plant was also investigated. The mass and energy balance of the bioprocess was simulated using Super-Pro Designer. The return on investments increased from -37.2% to 47.3% with scales increasing from 10 m<SUP>3</SUP> to 50 m<SUP>3</SUP>. Only the scales of 40 m<SUP>3</SUP> and 50 m<SUP>3</SUP> could get positive benefits with payback periods of 9.7 years and 6.9 years, respectively. The internal rate of return of scales of 40 m<SUP>3</SUP> and 50 m<SUP>3</SUP> were 0.63% and 9.25%, respectively, which meant the hydrogen-producing plant with higher scale (50 m<SUP>3</SUP>) would be more economically feasible.