To determine the optimal pH conditions and pH adaptation mechanisms of the juveniles new sea cucumber (Apostichopus japonicus) variety "Shenyou No.1", the differences in the growth, survival, respiratory metabolism, and immunoenzyme activity were analyzed under conditions of different pH (range: 6.5~10.0). The results showed that in the pH range of 6.5~9.5, the survival rate of the juveniles was 100% during the 30 days experimental period, whereas all juveniles died at pH 10.0. Within the pH range of 7.5~8.5, the juveniles showed a positive specific growth rate (SGR), and the highest SGR was 0.541%/d at pH 8.0, while the SGR was negative at the pH lower than 7.0 or higher than 9.0. The oxygen consumption rate (RO) and ammonia excretion rate (RN) were the lowest at pH 8.0, 19.07 μg/(g·h) and 1.34 μg/(g·h) for RO and RN, respectively. The oxygen-nitrogen ratios of the juveniles in different pH groups were approximately 11, and did not differ significantly with a pH change. The activities of acid phosphatase, alkaline phosphatase, lysozyme, and superoxide dismutase in the coelomic fluid of A. japonicus significantly increased at different pH values. While adapting to pH stress, the superoxide dismutase activity in each pH group generally peaked at 0 d, while the lysozyme activity peaked at 10 d. The survival pH of "Shenyou No.1" ranged between 6.5~9.5, and the optimal pH for growth ranged between 7.5~8.5. Our results show that the changes in the pH lead to changes in respiratory metabolism and immune enzyme activity in "Shenyou No.1.” These results provide the basis for the popularization of the new sea cucumber variety "Shenyou No.1".