Experiments were conducted to evaluate the effects of different salinity on growth, non-specific immunity and antibacterial activities of sea cucumber Apostichopus japonicus. The results showed that: (1) The survival rate of treatment A (salinity 16) was reduced to 66.7% (P<0.05), which was significantly different with other treatments and the control (P＞0.05). During the experiment, no mortality of sea cucumber was observed among the treatments at salinity of 22 and above. The specific growth rate of sea cucumber showed significant difference between treatments and control (P<0.05). At salinity of 20 and below, sea cucumber showed a negative growth. (2) The activities of superoxide dismutase (SOD), lysozyme (LZM) and antibacterial activity decreased with time, that is, from the maximum values at the beginning of the experiment to the minimum values at 30 d. We conclude that low salinity stress can significantly affect the survival and growth of sea cucumbers by reducing the immunity and increasing the susceptibility to pathogens, resulting in disease and mortality.