Abstract: A high-concentration anaerobic fermentation apparatus includes a liquid accumulation tank, a fermentation vessel, a feeding assembly, and a biogas residue collecting bin. The feeding assembly includes a hopper and a return conveyor belt including a first portion extending downward from the hopper till below a liquid level, a second portion extending upward from a bottom end of the first portion till above the liquid level, a third portion extending downward from a top end of the second portion till the liquid level, and a fourth portion extending upward from a bottom end of the third portion till out of the liquid level and above the biogas residue collecting bin. A pressure-feed flange is disposed at an outer side of the fermentation vessel, a feed channel is formed between the pressure-feed flange and the first portion, and a discharge channel is formed between the pressure-feed flange and the fourth portion.