Apostichopus japonicus Selenka with initial body weight (wet weight) of (3.5±0.1) g was reared in a 40 L glass tank (53cm×28cm×34cm) at water temperature of (17±0.5)℃ at a density of 4 ind./tank (group L), 8 ind./tank (group ML), 16 ind./tank (group MH) and 32 ind./tank (group H), and fed with diets supplemented with 0%, 1%, 3% and 5% Trp for 75 days with four replicates to investigate the effects of dietary Trp on growth and metabolic enzyme activities of Apostichopus japonicus Selenka reared at various densities. The body weight change and metabolic enzyme activities of Apostichopus japonicus Selenka were determined in the experiment. The results showed that the biomass of Apostichopus japonicus Selenka was increased and weight gain decreased as the stocking density increased. The maximum biomass was 196.1g (group H, 3% Trp), while the minimum weight gain was 35.9 (group H, 5% Trp). There was significantly higher growth rate in the Apostichopus japonicus Selenka fed with the diet containing 3% of Trp than that in the control group. The Apostichopus japonicus Selenka fed with the diet containing 3% of Trp had lower ALT activity, AST activity, MDH activity and LDH activity than that in other treatment groups at various stocking densities. The ALT activity, AST activity, MDH activity and LDH activity were 5.56 U/gprot, 1.85U/gprot, 0.17U/mgprot and 64U/gprot respectively when the diet containing 3% of Trp in H group, which were lower than those in the control group. The study showed that addition of 1%-3% dietary Trp could alleviate the stress of high-density culture on Apostichopus japonicus Selenka and improve the growth of Apostichopus japonicus Selenka.